30114008119961 THE ROYAL COLLEGE OF 8UR&tUK3 OF £Na Glasgow University Library — GUL 1 2 A MAR 1999 ALL ITEMS ARE ISSUED SUBJECT TO RECALL GUL 96.18 DESCEIPTIVE AND ILLUSTEATED CATALOGUE OP THE PHYSIOLOGICAL SERIES OF ' . COMPARATIVE ANATOMY CONTAINED IN THE MUSEUM OF THE ROYAL COLLEGE OE SURGEONS OE ENGLAND. VOL. II. SECOND EDITION. LONDON: PRINTED FOR THE COLLEGE; AND SOLD BY TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET. MDOCOOII. CONTENTS. VOL. 11. D. NERVOUS SYSTEM. INVERTEBRATA. ECHINODEEMATA. Nos. OPHIUROIDEA 1 ECHINOIDEA 2 HOLOTHUEOIDEA 3 ANNELIDA. OH^TOPODA 4—8 HIEUDINEA 9 GEPHYEEA 10 ARTHEOPODA. * OEUSTACEA 11—20 ARAOHNIDA 21—23 MYEIAPODA 24—26 INSECTA 27—39 MOLLUSCA. PELEOYPODA 40—43 AMPHINEUEA 44—45 GASTEOPODA 46—58 CEPHALOPODA 59—64 PROTOCHORDATA. TUNICATA . 65 CEPHALOCHORDA 66 VI CONTENTS OF VOL. II. VERTEBRATA. BRAIN. PISCES. 1^08. CYCLOSTOMI ; 67 ELASMOBRANCHII. Sqtjalida 68 81 IUjida 82—84 HOLOOEPHALI 85 GANOIDEI -86. TELEOSTEA. Anacanthini 87 — 96 acanthopteetgii 97 105 Phartngosnathi 106 Phtsostojii 107 — 118 Plectognathi 119 DIPNOI 120—121 AMPHIBIA. URODELA 122—125 ANURA 126 REPTILIA. LACBRTILIA . 127 OPHIDIA 128—132 ORNITHOSAURIA 133 DINOSAURIA 134 EMYDOSAURIA 135—139 OHELONIA . 140—147 AVES. STRUTHIONIFOEMES 148—157 ANSERIFORMES 158—173 FALOONIFORMES 174—182 CORACIIFORMES J 83 PASSERIFORMES 184—188 MAMMALIA. MONOTREMATA. Omiihorhynchidm 189 — 190 Echidnidce 191—196 CONTENTS OF VOL. II. vii MAES DPI ALIA. POLYPEOTOBONTIA. ]^08. Basyuriclce 197 — 203 Per-amelidce ' 204 — 206 Didelphijidce 207 — 208 DiPEOTODONTIA. Macropodidce 209 221 PhascolomyidcB 222 224 Phalangeridce 225 229 INSECTIVOEA.. Erinaceidce 230 ■ 231 Talpidce 232 Tupaiidce 233 Oentetidce 234 Deemoptera. Galeopitliecida 235 236 EODENTIA. SCIUEOMOEPBA. Castoridce 237 241 Scmridce . . . ,, 242 244 Htsteicomoepha . Octodontidce 245 Hystricidai 246—248 Ghinchillidce 249 251 Dasyproctidce 252 253 Gaviidce 254—257 Myomokpha. Dipodidcp. 258 Muridce 259 260 DtJPLlCIDENTATA. Leporidce 261—265 CHIROPTEEA 266 EDENTATA. Dasypodida; 267—270 Glyptodoniida; 271 272 Bradypodidce 273 278 Megatheriidce 279 280 Myrmecophac/idce 281—286 Manidce 9g'j' Orycteropidte 288 289 CONTENTS OF VOL. H. CARNIVORA. iELUKOIDHA. NOS. FeliclLH 290—300 Viverndce '301 — 314 fjycenidcp. 315 — 321 CrNOIDEA. Canidce 322—334 Arctoidea. Frocyonida' 33o — 348 MiisteNdce 349—359 Ursida- 360—369 PiNNIPBDIA. Otariidce 370 — 374 Phocidce 375 — 386 UNGULATA. Htkacoidea 387 — 389 Ambltopoda 399 Probosctdea 391 — 392 toxodontia 393 Perissodacxyla. Tapiridoe 394—398 Bhinocerotidce 399—402 Equidce 402—407 ABTIODACTrLA. Snidce 408-413 Dicotylidce 414—416 Hippopotamidcii "^1' '^^^ Camelidce. 420-423 TraguUdoi 424—428 Cervidce 429—451 Oiraffidce 452—453 Antilocapridce ^54 Bovidce 455—505 SIRENIA 506—510 OETACEA. Odontocbti. Delphinida; 511—521 Physeterider. ^22 CONTENTS OF VOL. II. ix Mtstacooeti. Nob. Balcenidce 523—530 PRIMATES. Prosimii. CTiiromyidce 531 — 532 Lemuridce 533 — 548 Anthkopotdba. Hapalidce 549 — 553 Cehidce 554—593 CercopitJiecidm 594 — 643 Simiidce 644 — 674 HominidcB 675 — 728 Membranes of the Brain 729 — 740 Blood-vessels of the Brain 741 — 748 SPINAL CORD. PISCES. CYOLOSTOMI 749 ELASMOBEANOHir 750—752 TELEOSTEA 753—755 AMPHIBIA 756—757 EEPTILIA 758-764 AYES 765—771 MAMMALIA. MONOTREMATA 772—773 INSEOTIVORA 774 EDENTATA 775—776 OARNIVORA 777—780 UNQULATA 781—790 OETAOEA 791—796 PRIMATES 797—805 Membranes of the Spinal Cord 806—808 VOL.' n. h I I DESCEIPTIVE CATALOGUE OF THE PHYSIOLOGICAL SERIES. D. NERVOUS SYSTEM* INVERTEBRATA. Loeb, Comparative Physiology of the Brain, 1901. ECHINODEEMATA. NCudnot, Arch, de Biol., t. xi. 1891, p. 445 {Anat.). ^Romanes & Ewart, Phil. Trans., vol. clxxii. 1881, p. 836 ' (Physiol.) . In the Echinodermata there are three distinct systems of central nervous organs— superficial oral, deep oral, and apical— that occur, either in the form of a circumaxial ring (apical system of Echinids and Ophiurids), radial cords (apical system of Asterids and deep oral system of Holothurians), or more usually as a combination of the two (superficial oral system). All three are not invariably present, and there is also variation in their respective importance. The superficial oral system occurs in all and usually pi-edominates over the others, but in Crinoids it is relatively weak and the chief place is taken by the enormously developed apical system. The apical and deep oral syst ems are * In this volume are included descriptions of the nervous system of Invertebrata and Protochordata and of the brain and spinal cord, with their membranes and blood-vessels, of Vertebrata. VOL. II. R 2 PHYSIOLOGICAL SERIES. sometimes absent. The whole central system, whether it is continuous with the general body-epithelium (Asteroidea) or is comparatively deep-seated, always retains strong indications of its epithelial origin. Two kinds of nuclei lie in the super- ficial parts of the nerve-cords — some large and with distinct nucleoli, belonging apparently to ganglion-cells, others 'small and deeply-staining. The latter belong to attenuated supporting epithelial cells that traverse the cord at right angles to its surface. The spaces between them are filled by nerve-fibrillse. Fig. 1. Transverse section through the Radial Cord of Hchintis esculentus. X 700. C.L. Connective-tissue lamina. Q.C. Nuclei of ganglion (?) cells. S.C. Supporting cells, N.F. Nerve-fibrils. Isolation of the several radial cords of the oral system from the circumoral ring destroys all power of co-ordinated action between the different arms or segments, although the move- ments of the individual parts of each are still in perfect harmony amongst themselves. From this fact the circumoral ring might be thought to be a co-ordinating centre for the general body movements, and thus of somewhat higher functional value than the radial cords, but it is probably nearer the truth to consider all parts of the system of equal value and the circumoral ring simply as the path along which stimuli may pass from one segment to another. OPHIUEOIDEA. D. 1. Two specimens of the oral central nervous system of a Snake-armed Starfish {Ophiocoma echinata). The superficial oral system consists of a pentagonal ring that surrounds the mouth near its passage into the NERVOTJS SYSTEM. — INVERTEBRATA. 3' oesophagus, and o£ five radial cords. Each cord arises from the ring at {i point opposite one of the radii and passes down the arm between the vertebral ossicles- and the ven- tral plates (fig. 2) . A"cavity (epineural canal) lies between Pig. 2. ^ ^ I -t P. V. Diagrammatic transverse section of the Arm of Ophiocoma echinata. x40. A.V. AmtiUacral vessel. E.G. Epineural canal. M. Intervertebral muscle. P. Median partition of epineural canal. P.V. Pseud- haemal vessel. E.G. Radial cord. T.F. Tube-foot. V. Vertebral ossicle. V.P. Ventral plate, the body-wall and the superficial surface of the oral ring and radial cords ; it is usually single, but in Ophiocoma a partition of connective tissue divides it longitudinally into two separate channels. The superficial oral system is to a large extent sensory in function; it innervates the entire body surface, the ambulacra, the mouth, and aHmentary canal. The deep oral system (not distinguishable in the specimen) forms a thin layer of nervous tissue upon the deep surface of the superficial system, separated from it by a delicate layer of connective tissue. Upon its deep surface lie the pseud- hsemal and ambulacral vessels. The deep oral system is the motor centre for the intervertebral muscles of the arms, and probably also gives off fibres that accompany the peri- pheral and ambulacral nerves of the superficial system. 'J'he oral ring and proximal parts of the radial cords are shown in an isolated state in the upper specimen, and in B 2 4 PHYSIOLOGICAL SERIES. their relations to the disc in the lower ; in both cases only the most general features can be seen. . The apical system has been removed with the genital ring sinus in which it lies. 0. C. A 1292 C. Bnt. Mus. Hamann, Jena. Zcitschr., Bd. xxiii. 1889, p. 23.5. EcnmoiDEA. D, 2. Part of the body- walls of a Sea-urchin [Echinus esculentus) showing the oral nervous system. The superficial system corresponds in its main features to that of Ophiurids. The oral ring (indicated by black paper) lies around the mouth-opening between the teeth and the pharyngeal wall, separated from the latter by an epineural canal. Opposite each of the five radii it gives off a cord that leaves the lantern of Aristotle between the pyramids, passes under the arch of the auricula, and runs along the mid-line of the radius, separated from the inner surface of the ambulacral plates by an "epineural canal," and from the general body-cavity by the radial canals of the pseudhsemal, blood-vascular, and ambulacral systems. Near the apical pole the cords pass through the test and become lost in the general surface epithelium. From the oral ring a few fine nerves are given off to the alimentary canal, and from the radial cords arise a series of ambu- lacral and peripheral nerves. The latter perforate the test and form upon its outer surface an intricate plexus, by which the movements of the spines and pediceliarige are controlled. The deep oral system (not visible in the sijecimen) is in a reduced condition, and is only present upon the inner surface of the oral ring at the point of origin of the radial cords ; it innervates the masticatory apparatus, and is entirely wanting" in agnathous forms. In this specimen parts of the oral systems have been exposed, showing the circum-oral position of the nerve-ring and its relation to the radial cords. One of the latter with its ambulacral nerves has been isolated by the removal of the ambulacral plates of one radius. The apical system has been removed with the genital-ring sinus. Hamann, Jena. Zeitschr. Bd. xxi. 1887, p. 119. NERVOUS SYSTEM. — INVBRTEBKATA. 5 HOLOTHUEOIDEA. D. 3. A Sea-cucumber [Ilolothiria nigra) with the nervous system shown by the removal of the bivial body-walls. The oral ring of the superficial system surrounds the . mouth under cover of the calcareous ring and in close contact with the oral integument. The five radial cords given oflf from it pass beneath the radial pieces of the cal- careous ring and along the radii; they are separated from the deep surface of the integument by an epineural canal. The deep oral system (not visible in the specimen) is confined to the inner surface of the radial cords, and is separated from the muscles of the body-wall by the pseud- htemal, blood-vascular, and ambulacral vessels. The re- spective share taken by the two systems in the innervation of the body has not been satisfactorily determined. There is no apical system. Black paper has been inserted beneath the oral ring at the points of origin of the radial cords and in various places beneath the cords. The calcareous ring has been removed. 0. C. A 1292 h. Ludwig, Bronn's Thier-reich, Bd. ii. Abth. 3, 1889- 1892, p. 64 ANNELIDA. Ketzius, Biol. Untersuch., N.F. Bd. ii. p. 1, iii. p. 1, iv. p. 1, vii. p. 6, ix. p. 83, 1891-1900. The central nervous system is bilaterally symmetrical ; it consists typically of a pair of prseoral (cerebral) ganglia situated in the prostomiiim, and of a series of post-oral ganglia, arranged segmentally in pairs along the ventral mid-line of the body and united together by transverse commissures and longitudinal connectives. This ventral chain of ganglia shows great diversity in the degree of concentration of its parts in a transverse direc- tion. Longitudinal concentration is rare and never extreme. Frequently the segmental ganglionation is absent, and the chain is then represented by a fibrous cord with a continuous layer of ganglion-colls on its ventral surface. The size and complexity of structure of the cerebral ganglia depend entirely upon the degree of development of tlie cephalic sense-oH^ans. Apart from particular functions due to their counectio'A''%ith 6 PHYSIOLOGICAL SERIES. these organs, they do not seem to differ in kind from the post- oral ganglia, and, except for a certain inhibitory power, cannot be regarded in any special way as controlling or co-ordinating centres for the rest of the nervous system. Each pair of ventral chain ganglia constitutes a reflex centre for its innervation area. In the ventral chain of many Annehds there are a limited number (usually three) of medullated giant nerve- tubes ; in many instances connections have been seen between them and giant or medium-sized cells upon the ventral suTface of the ganglia. Their function is still doubtful, but they are probably nerve-elements and not simply supporting structures. A definite visceral system is present connected with the cerebral or suboesophageal ganglia. In certain forms the central nervous system is still closely united to the epidermis (subcuticula), and in these cases the fibres of its supporting tissues can be traced directly to the elongated bases of the epidermal cells. CH^TOPODA. Racovitza, Arch. Zool. Exp., ser. 3, t. iv. 1896, p. 133 [Brain) . D. 4. The anterior part of the body-walls o£ a Lug-worm [Arenicola marina) opened from the dorsal aspect. The nervous system, as might be expected from the sluggish habits of the worm, is poorly developed. The cerebral ganglion is a small lobulated body situated, as in other Polychsetes, in the prostomium (in the specunen the anterior part of the body-wall is turned inside out, so that the cerebral ganglion and inverted prostomium form a small excrescence above the cut edge of the pharynx). There are thyee distinct paired centres in the ganghon, constituting a fore-, mid-, and hind-brain ; each is situated beneath and in close contact with a particular sensory area of the prostomial epithelium, upon which labial palps, tentacles and eyes, and a nuchal organ may respectively be developed in higher Polychfetes. The cerebral ganglion is connected by a pair of long connectives (from which the nerves to the otocysts ari.'^e) to a ventral cord, that lies within the body-cavity internal to the circular muscles; NERVOUS SYSTEM. — INVERTEBRATA. 7 it shows no sign of metameric ganglionation, but on a level with each annular furrow gives off a delicate pair of nerves. Neuropile* appears to be mainly confined to the cerebral oanolion. The medulla of the cord consists of a dorsal strand of nerve-fibres, covered on its ventral surface by a continuous layer of unipolar ganghon-cells, mostly of small size (fig. 3) . At the point of union of the cord with Fig. 3. NL. P. G.F. Nl, G-C- CM. Transverse section through the Ventral Cord of Arenicola marina. X 50. CM. Circular muscles. G.C. Ganglion - cells. G.F. Giant fibres. L.M. Longitudinal muscles. M. Medulla. N.L. Neurilemma. N.S. Neuroglia septum. P. Peritoneum. the oesophageal connectives and on a level with the anterior end of each setigerous segment, are a pair of giant ganglion- cells. In several instances a direct connection has been traced between these cells and three giant -fibres that lie along the dorsal aspect of the cord. The distribution of the giant fibres is still doubtful. The cord is surrounded by a neurilemma, and is permeated by a considerable quantity of neuroglia fibres. These are specially concen- trated in the sagittal plane, and form a partial septum between the two halves of the cord. In the specimen the general form and position of the cerebral ganglion, circum- oesophageal connectives, and ventral chain can be seen, but * The felt-work formed by the ultimate ramificiitious of ganglion-cell 8 PHYSIOLOGICAL SEKIES. it is not possible to distinguish the nerves arising from them. Gamble & Ashworth, Quart. Journ. Micro. Sci,, vol, xliii. 1900, p. 468. D. 5. Two specimens of the anterior part of the nervous sj^stem of a Polychsete {Marphysa aanguinea) , shown respectively in an isolated state and from the left side within the body. In this active worm, with definite cephalic 'sense-oroans the cerebral ganglia are well developed (fig. 4). Thev lie in the prostomium at the base of the swollen palps, and are clearly separable into two main region.s — fore- and mid-brain — each of which consists of a pair of neuropile masses united by a transverse commissure, and coated with Fig. 4. p. L , Brain of Maiyhysa sanguinea. x 25. A.N, Antennary nerves. E. Eye. F.B. Fore-brain. F.C. Its com- missure. H.B. Hind - brain. L.M. Longitudinal muscles M.B. Mid-brain. M.C. Its commissure. O.N. Optic nerve CES.O. (Esophageal connective. P.L. Palp-lobules. V.N, Vis- ceral nerve. small unipolar ganglion-cells. The fore-brain lies in front of and below the mid-brain, and is mainly concerned with the innervation of the palps, into which the anterior part of each of its lobes is prolonged as a bundle of arborescent ganglionic processes. Each lobe also sends a root from its ventral surface to the visceral nerve, and another from its lateral parts to the circumcesophageal connective. NERVOUS SYSTEM. — INVEliTEBRATA. 9 The mid-brain is the centre of origin for the nerves to the eyes and tentacles. Its postero-lateral parts are pro- longed backwards to form a pair of indistinct lobes, from which fibres extend to the nuchal region — they apparently represent the third area of the Polychaate brain (hind- brain). From each side of the mid-brain a second root is given oflf to the circumoesophageal connective ; it unites Fig. 5. Transverse .section tlirough a Ventral-chain Ganglion of Marphysa sanguinea. X 76. CM. Central medulla. O.T. Oonnective tissue. G.C. Ganglion-cells. G.F. Giant fibre. L.M. Longitudinal muscles. N.R. Nerve- root. • P.G. Pigment masses. with the first (derived from the fore-brain) immediately outside the ganglion. The ganglia of the ventral chain lie close together, one in each segment, and are united by definite though short fibrous connectives. A pair o£ para- podial nerves rises from each ganglion. Upon the ventral surface of the cord runs a single large " giant fibre.^' Jourdan, Ann. Sci. Nat., ser. 7, t. ii. 1887, p. 250. D. 6. Two specimens of the nervous system of a Sea Mouse {Aphrodite aculeaiu). The cerebral ganglion is of large size and complicated structure ; it lies in the prostomiuin and consists of a central mass of neuropile, separable into two main centres — the fore- and mid- brain. Between the two, on their posterior surface, lies a third, very definite mass of neuropile, from which a pair of stalk-like processes project upwards towards the dorsal integument. Each stalk 10 rHYSIOLOGICAL SERIES. expands somewhat at its distal end and is capped hy a number of closely packed nuclei, surrounded by a limited amount of protoplasm. Small ganglion-cells of a similar nature (ganglionic nuclei) are found in connection with the sensory centres in many Invertebrates, and in this instance they complete the striking resemblance that these stalked structures bear to the fungiform bodies of Insects. It is to be noticed that the neuropile at the base of the stalks is condensed here and there to form glomeruli similar to those found in the olfactory centres of Arthropods and Fig. 6. M.B. G.N. , . ^, „ „ GL. ST. Kb. Transverse section through the Brain of Aphrodite actdeata. X 50. 0. Root of oesophageal connective. F.B. Fore-brain. G.C. Ganglion- cells. GL. Glomeruli. G.N. Ganglionic nuclei. M.B. Mid- brain. S. Stalk of " fungiform body." S.T. Supporting tissue. Vertebrates. The relations of the "fungiform bodies" to the cephalic sense-organs is doubtful. The cerebral ganglion is enclosed in a thick capsule composed of large granular stellate cells lodged within a loose vacuolated connective tissue ; a protecting and supporting layer of somewhat similar structure is present around the cerebral ganglion and ventral cord of Gephyrea. In the meshes of this tissue lie a number of moderate-sized ganglion-cells, forming a sparse layer around the brain. A pair of long slender connectives pass on either side of the pharynx to the anterior ganglion of the ventral chain. Each arises by two roots derived respectively from the fore- and mid- NERVOUS SYSTEM. — INVERTEBRATA. 11 brain. The ganglia of the ventral chain are transversely concentrated and sliow^ no external sign of their paired nature ; they are metamerically disposed and united to one another by a pair of closely approximated connectives. Each ganglion gives off three pairs of nerves, the largest of which arises furthest back and innervates the parapodia, while the two anterior pairs supply the trunk muscles and skin of the segment in which the ganglion lies. All parts of the ventral chain are enclosed in a thick fibrous neuri- lemma (subcuticular fibrous tissue), on the outer surface of which there is a delicate homogeneous membrane (fig. 7). Fig. 7. S.F. .L. Part of a Ventral-chain Ganglion of Aphrodite aculeata in transverse section. X 150. CM. Central medulla. G.O. Ganglion-cells. H.M. Homogeneous membrane. N.L. Neurilemma. S.F. Supporting fibres. Many delicate fibres derived from the neurilemma traverse the substance of the connectives and ganglia. Ganglion- cells are confined to the ventral surface of the ganglia; they are lodged in the meshes of the neurilemma. In the upper specimen the anterior portion of the nervous system including the brain and 7 ventral chain ganglia is shown in an isolated condition. Below is an entire animal in which the nervous system is displayed in situ hy the removal of the ventral body- walls from the mid-lino. Rohde, Zool. Beitr., Bd. ii. 1890, p. I. 12 rHYSIOLOaiCAL SERIES. D. 7. Two specimens o£ the nervous system of an Earthworm {Lumhricus terrestris) showing the anterior part isolated and the whole system in situ. The cerebral ganglion is small and bilobed. It is situated above the posterior part of the buccal cavity in the third bod}'- segment, and is united by a pair of fibrous connectives to the ventral cord. The latter lies free in the body-cavity, and swells slightly within each segment to form a ganglion, from which three pairs of nerves are given off to the bod} -walls. Between the ganglia, the cord is almost, though not quite, free from Fig. 8. G.F. N.L? /T\ Transverse section through a Ventral-chain Ganglion of Lumbricm terrestiis. X 125. B.L. Blood - vessel. CM. Central medulla. G.O. Ganglion - cells. G.F, Giant fibres. M. Muscle-fibres. Nh\ NL'-. The two layers of neurilemma. S.T. Supporting tissue. ganglion-cells. The central nervous system is surrounded by a neurilemma, in which two Liyers are distinguishable : (i.) an outer layer largely composed of longitudinal muscle- fibres, (ii.) an inner cuticular layer. Within the cuticle lie the connectives and ganglia embedded in a supporting fibrous tissue (? neuroglia) (fig. 8). Three medullated giant fibres run along the dorsal surface of the cord ; their relations to the rest of the system are still obscure, but it is certain that at the hinder end of the cord the two lateral NERVOUS SYSTEM. — INVERTEBRATA. 13 fibres are in connection with ganglion-cells that lie in pairs on the ventral surface of a certain number of the posterior ganglia of the chain. Anteriorly the lateral fibres are said to break up in the suboesophageal ganglion. The median fibre apparently arises from cells in the same ganglion. Branches from all three fibres have been seen to enter the lateral nerves. It is probable that the giant fibres act as a direct path of communication between all regions of the nervous system, and are. particularly concerned in bringing about the simultaneous contraction of the whole body-wall, such as takes place when the worm shoots back into its burrow. In creeping, contraction occurs slowly segment by segment. The co-ordination of this segmental contrac- tion is apparently due, not so much to connections within the central nervous system as to an orderly sequence of independent stimuli, each of which is caused by the stretching of the integument of any one segment by the contraction of the longitudinal muscles of the segment in front. Friedlander, Zeits. wiss. Zool., Bd. xlvii. 1888, p. 47, & Bd. Iviii. 1894, p. H61 (Anat.). Friedlander, Arch. ges. Physiol., Bd. Iviii. 1894, p. 168 (Physiol.). D. 8. An Earthworm (Lumhricus terrestris) with the ventral body-walls removed to show the nervous cords, their ganglia and lateral branches. 0. C. 1296. Hunterian. HIETJDINBA. D. 9. The ventral body-walls of a Leech [Ilirudo medicinalis) with the nervous system exposed from the dorsal aspect. The central system lies amongst the parenchyma internal to the body-walls. The cerebral ganglion is a small bilobed body situated close behind the jaws on the upper surface of the pharynx ; it is of very simple construction and probably, as its removal causes no appreciable difference in the actions of the animal, differs little if at all in function from the giinglia of the ventral chain. It innervates the cephalic sense-organs, and jaws. A pair of extremely short connec- tives unite the cerebral ganglion around the anterior part of 14 PHYSIOLOGICAL SERIES. the pharynx to a series of (apparently) 23 transversely concentrated ventral-chain ganglia. The first of these (subcDSophageal ganglion) is of some size and represents the four anterior ganglia of the chain ; the following 21 are simple rounded masses, situated segmentally, and each giving off two pairs of nerves to the body-walls of its seg- ment. The terminal ganglion is a compound structure like the first, and represents a longitudinal concentration of at least 7 pairs of ganglia ; it supplies the anal sucker. The successive post-oral ganglia are united to one another by three connectives — a lateral pair similar to those of other worms and a delicate median ventral cord (nerve of Faivre) Fig. 9. M. Transverse section through the Ventral-chain Connectives of Hirudo medicinalis. X 200. B.S. Blood-space. C. Connectives. M. Muscle-fibres. N.F. Nerve of Faivre. NL', NL". The two neurilemma-sheaths. P.C. Pig- ment-cells. S. Septa. that originates in the suba2sophagcal ganglion and extends throughout the length of the chain ; it is lost in the dorsal parts of each ganglion (figs. 9 and 10). Each simple post-oral ganglion consists of a laterally paired mass of neuropile, invested on its lateral and ventral surfaces by unipolar ganglion-cells of different sizes. Two of these at the anterior end of the ventral surface of each ganglion are of colossal proportions ("1 mm. diam.), and contribute fibres to the lateral nerves o£ the same side. NERVOUS SYSTEM. — INVERTEBRATA. 15 There are no giant fibres in the connectives. The ventral cord is surrounded by a double neurilemma -sheath — (i.) an outer sheath that loosely envelopes the cord and extends for some distance along the lateral nerves : it forms the outer wall of the perineural blood-vessel ; (ii.) an inner sheath, that closely invests the cord and binds the three connectives into a single strand. Offshoots from Transverse section through a Venti-al-chain Ganglion of Hirudo medichialis. X 125. CM. Central medulla. G.C. Ganglion-cells. G.GO. Giant ganglion-cells. this inner sheath penetrate amongst the fibres of the con- nectives and dip into the substance of the ganglia, where they separate the ganglion- cells into three definite groups and form an investment to the central medulla. Both sheaths contain many muscle-fibres. The outer neurilemma-sheath has been removed and black paper placed beneath the nerve-cord. 0. G. 1295 b. Leuckart, Die Parasiten des Menschen, Bd. i. 1894, p. 579. GEPHYEEA. D. 10. The anterior and posterior parts of the body-walls of a Gephyreaa {Sipunculus nudus) showing the nervous system. The cerebral ganglion is a rounded mass with slight lateral swellings, situated upon the dorsal surface of the oesophagus at the base of the tentacles. Nerves for the tentacles arise PHYSIOLOGICAL SERIES. from its postero-lateral surface, and upon its anterior face are a number of finger-like processes of doubtful function (possibly sensory). It has been shown that a special reflex connection exists between the cerebral ganglion (a purely sensory centre ?) and the motor centre that controls the retractors of the introvert. Two long (11 mm.) circum- oesophageal connectives (from which the nerves for the retractors of the introvert are given off) unite the cerebral ganglion to the ventral cord. The latter for the first part of its course lies loose in the body-cavity accompanied by a strand of muscle (mostly removed in the specimen) ; about 10 mm. in front of the nephridia it becomes closel}- applied to the body-wall, and runs in this position between two bundles of the longitudinal muscle-layer to the posterior extremity of the body, where it terminates in a spindle- shaped enlargement. So long as the ventral cord lies close to the body- wall it gives off, about the middle of each circular muscle-band^ a pair of lateral nerves, that run between the circular and diagonal muscle-layers towards the dorsal mid-line, but do not meet to form a complete ring round the body. In front of the nephridia the nerves come off more irregularly and are enveloped in strands of muscle; they supply the anterior end of the trunk and the introvert. No nerves arise from the cord within the introvert. The cord is a mixed motor and sensory centre in which impulses are slowly propagated (100-200 mm. per second) in either direction. The cerebral ganglion consists of a central mass of neuro- pile surrounded by unipolar ganglion-cells varying in size from 4-55 fi, and arranged in fairly definite groups ; a few bipolar cells occur in the neighbourhood of the digitiform processes. The substance of the ganglion is permeated by a network of neuroglia fibres, and it is enclosed in a pro- tective layer of large stellate cells (neuroglia cells ?). The cord is composed of a fibrous core covered on its ventral surface by ganglion-colls ; it shows no sign of ganglionation or lateral duplicity. It is surrounded by a double sheath of neurilemma, the space between the two being filled with stellate cells similar to those around the cerebral ganglion. The posterior enlargement does not differ in structure from NEEVOUS SYSTEM.— INVKRTBBEATA. I7 the rest of the cord : its size is mainly due to an increase of the stellate cells between the neurilemma-sheaths. In the specimen the introvert is retracted. A red rod has been placed in the month and black paper beneath the different pai'ts of the nervous system. Metalnikoff, Zeits. wiss. Zool., Bd. kviii. 1900, p. 293 (Anat.). Uexkull, Zeits. Biol., N.F. Bd. xv. 1896, p. 1 (Physiol.). ARTHROPODA. Bethe, Arch. £. ges. Physiol., Bd. Ixviii. 1897, p. 449 (Physiol.). The central nervous system agrees with that of Worms in its bilateral symmetry and general plan of construction, but is always entirely free from the integument. The cerebral gan ^lion IS comparatively simple in many cases, but shows a gradual increase m size and complexity of structure as the cephalic sense organs become more perfect and the intelligence more pro- nounced. This brain development is noticeable in the increasing comphcation of the optic ganglia and in the development of glomerular condensations in the neuropile of the antennary lobes very similar to those in the olfactory lobes of Vertebrates, but IS particularly marked by the appearance, among the higher orders, of peculiar cerebral organs (fungiform bodies) whose development seems to be linked in some obscure way with the growth of the intelligence. The visceral system is always clearly defined. Its centres of origin (oesophageal ganglia) show a gradual migration from their original post-oral position to- .vards the cerebral ganglion, and finally fuse with it. although always united by a post-oral commissure. The ventral chain m all except the lowest groups shows a considerable degree of concentration laterally, but varies in longitudinal concentration ^vlth,n the widest limits-from the Phyllopods with a pair of ganglia to every pair of appendages, to the Brachyura, some Arachnids and Insects, in which it is represented by a single post-oral ganglionic mass. The segmental character of the nervous system is functional as well as structural, for each ganglion forms an independent reflex centre for the activities of its innervation area. Co- ordination is mainly due to transmission of stimuli from ganglion VOL. II. • ° ° C 18 PHYSIOLOGICAL SEIHES. to gancrlion, bnt also, at least as concerns locomotive movements, to the influence ol: a definite centre of co-ordination— the subceso- phageal ganglion. The cerebral ganglion exerts a higher conh-olling influence over the rest of the system than in Worms, owing to its increased inhibitory power and to the production of the general muscle tonus (state of constant partial contraction). It is hard to say whether any power of initiation should be assigned to the cerebral ganglion— its removal generally results in the cessation of spontaneous locomotion, but this may be due to decrease in muscle-power following upon loss of tonus. ORUSTAOEA. D. n. The isolated nervous system of a Phyllopod (Apus productus). The central system is in an essentially primitive Fig. 11. C,G. Diagram of the anterior parts of the Nervous System oiApus, after Zaddach and Pelseneer. A.CS A.C*. Centres for antennary nerves i. aYid it. A.N', A.N^. An- tennary nerves. (ES.G. CEsophageal ganglion. C.G. Cerebral ganglion. O.N. Optic nerve. V.C. Visceral centre. NERVOUS SYSTEM. — INVERTEBRATA. 19 condition, and reminds one, in the ladder-like construc- tion of its venti-al chain, of that of certain Tube-worms (e. g. Serpula). The cerebral ganghon is a small quadri- lateral body, situated in front of the oesophagus close beneath the eyes, and so placed that its proper ventral surface faces upwards and its anterior border backwards. It gives off a pair of nerves from the outer angles of its true anterior end to the eyes. The first pair of antenna? are supplied by a pair of small nerves that seem to rise from the circumoesophageal connectives ; their true centres of origin are, however, situated in the lateral parts of the cerebral ganghon. On a level with the posterior margin of the mouth, each circumoesophageal connective enlarges to form an oesophageal ganglion, which gives off two nerves —a small one from its outer aspect to the second antenna, and a visceral nerve from its inner surface ; thetwogangha are united by a double commissure. The condition^'of the antennary nerves in Apus suggests that the direct origin of these nerves in the higher Crustacea from the cerebral ganglion is the result of an anterior concentration of centres originally separate and post-oral in position. The gangha of the ventral chain are paired and, in the anterior region of the body, widely separate. They are united to one another transversely by a double commissure and longi- tudinally by a pair of connectives. In the posterior part of the body the ladder-like appearance of the chain is lost owing to the shortening of the commissures and connectives although the individuality of the ganglia is maintained.' The ganglia correspond in number and position to the appendages, and are thus more numerous than the body segments. The second pair of maxillte alone seem to have no corresponding ganglia; their nerves arise from the connectives. The specimen is so small that only the most important of the above-mentioned characters are visible, such as the wide lateral separation of the ventral-chain ganglia and their gradual approximation to one another posteriorly. q. C. 1302l. Pelseneer, Quart. Journ. Micro. Sci., vol. xxv. 1885 p. 433. ' 0 2 PHYSIOLOGICAL SERIES. 12 Two specimens of the nervous system of a Barnacle {Lepas ariatifera). The small bilobed cerebral ganghon lies on the anterior wall of the oesophagus at its entry into the stomach; it gives off a large nerve on either side to the peduncle, and an extremely fine pair (not visible m the specimens) from its anterior surface to the vestige.l eye. The visceral nerves arise from the circumoesophageal connectives close behind the cerebral ganglion. The sub- oesophageal ganglion is the largest and most important nerve-centre in the body ; it sends a large pair ot nerves from its dorsal surface to the adductor scutarura muscle, and also supplies the mouth-parts and first pair of cirri, li is followed by a chain of four segmentally placed ganglia, each of which gives off a pair of nerves to the cirri of its seo-ment; the terminal ganglion is slightly larger than the others, and represents a fusion of two, it innervates the last two pairs of cirri and the penis. The ganglia are moderately concentrated in a transverse direction, but^ the connectives-particularly at the anterior end of the chaiu- are distinctly separate. Between them runs a small median nerve (not visible in the specimens), that arises in the sub- oesophageal ganglion and is ultimately distributed to the rectum. In the upper specimen the nervous system is shown in an isolated state, and in the lower ^om the right side within the body. 0. U 1302 K. Gruvel, Arch. Zool. Exp., s6r. 3, t. i. 1893, p. 489. D. 13. A Stomatopod {Lysiosquilla, sp.) with the nervous system displayed from above. The small quadrilateral cerebral ganglion lies in the second cephaUc segment; it gives off three large pairs of nerves respectively to the eyes and to the two pairs of antennae, as well as a few delicate branches (not shown in the specimen) to the neighbourmg muscles and integument. The circumoesophageal con- nectives, owing to the extended character of the head- rerrion, are remarkably long in front of the mouth; on either side of the cBsophagus they swell slightly to form a pair of small oesophageal ganglia, that give off the visceral nerves and are united together behind the cesophagus by a single commissure. A short distance behind the oesophagus NERVOUS SYSTEM. — INVBRTEBRATA. 21 tlie connectives join the suboesophageal ganglion — an elongated mass formed by the longitudinal concentra- tion and fusion of eight jiairs of ganglia; it innervates the mandibles, maxillse, and five anterior pairs of thoracic a[)pendages. The last three thoracic and the six abdominal ganglia are segmental in position ; each gives off three pairs of nerves, distributed respectively to the appendages and lateral muscles of the same segment and to the flexor muscles of the one behind. The terminal ganglion supplies the sixth abdominal segment and the telson. All the ventral- chain ganglia show a high degree of transverse concen- tration, combined (except in the case of the suboesophageal ganghon) with well-marked longitudinal separation. The connectives are bound up in a common neurilemma-sheath. Bellonci, Ann. Mus. C!iv. Stor. Nat. Geneva, vol. xii. 1878, p. 518. D. 14. Two specimens of the nervous system of a Lobster {Homarus vulgaris). The cerebral ganglion is lodged immediately below the bases of the eye-stalks; it is roughly quadrilateral in shape, with a pair of conspicuous rounded eminences (globuli) upon its lateral margins. Each of its upper angles is connected by a nervous tract to a rod-shaped optic ganglion that lies within the eye- stalk ; from its lower angles arise the antennarj' and in- tegumentary nerves ; the circumoesophageal connectives are given olf from the middle of the ventral border. The cerebral ganglion, as in other Decapods, has considerable structural complexity (fig. 12). Three regions can be traced in it, of which the anterior two correspond probably to the proto- and deuto-cerebrum of the Insect brain, while the third is a part of the ti-itocerebrum peculiar to Crus- tacea. The protocerebrum is the optic centre ; it consists of the optic ganglia, and of a quadrilateral mass (prolo- cerebral lobes) that forms the upper part of the cerebral ganglion. The protocerebral lobes are separated by a slight median furrow; they are traversed by numerous commissural fibres, and have in the middle of their sub- stance a transverse bar of dense neuropile that probably represents the corpus centrale of the Insect. 22 PHYSIOLOGICAL SEMES. Eiicb optic ganglion contains four neuropile masses placed at intervals between the retina and the optic tract and united together by decussating fibres; upon the dorsal surface of the centre nearest the tract is a small excrescence that may possibly represent the fungiform body of the Insect brain in a very rudimentary state. There are two pairs of centres in the deutocerebrum — the lateral lobes (globuli) united by a stout commissure, Fig. 12. PC.L. ; ,' I: ,.c.PC.L •6'' DC. / C.'GB. GB. GL. Horizontal section through the Brain of Astacusjluviatilis. X 40. C.C. Corpus centrale. C.GB. Counnissure of globuli. C.PC.L. Com- auissures of protocerebrnl lobes. U.C. Ueutocerebruni. GB. Globulus. GL. Glomeruli. G.N. Ganglionic nuclei. O.D. Decussating bundle of optic tract. O.T. Optic tract. PC.L. Protocerebral lobe. T.C. Tritocerebrum. and, internal to them, two smaller neuroi)ile masses con- tiguous in the mid-line : each pair gives rise on either side to a root of the first :intennary nerve. The nature of the globuli is obscure ; some compare them with the fungiform bodies, others with the antennary lobes of Insects, in support NERVOUS SYSTEM. — INVEKTEBRATA. 23 of tlio latter view, it may be said that the globuli of Crusta- ceans agree with the antennary lobes of Insects in having glomerular condensations o£ their neuropile, in giving off a root to the antennary nerve, and in receiving a large decussating tract from the fungiform body of the opposite side, assuming such to be the nature of the protuberance on the optic ganglion o£ the Lobster. The tritocerebrum constitutes the centre for the second antennary and the tegumentary nerves. The complicated structure of the cerebral ganglion is apparently mainly due to its connection with highly developed sense-organs, yet the fact that its removal causes more disturbance to the normal activities of the creature than in Worms — particularly by destroying the capability of spontaneous locomotion — suggests that it possesses to some degree, at any rate, the power of controlling, or perhaps even o£ initiating, activities in the rest of the nervous svstem. ft/ A pair of small oesophageal ganglia are situated upon the circumoBSophageal connectives on a level with the (Bsophagus, but some distance in front of the post- ojsophageal commissure by which they are united. Each of them gives off, besides a few delicate filaments to the oesophagus, two stout nerves. One of these runs forward, parallel to the oesophageal connectives, half-way to the cerebral ganglion, and at this point unites with its fellow of the opposite side and with a median nerve derived from the cerebral ganglion, to form the gastric nerve — a trunk that runs in the median plane along the anterior and dorsal surfaces of the stomach to the pylorus, at which point it forms a small ganglion and divides into two lateral branches which are distributed to the intestine. The second of the two nerves supplies the upper lip and is connected by a branch to the components of the gastric nerve where they unite to form the median trunk. The suboesophageal ganglion innervates the mouth appendages and gives off from its dorsal surface a few nerves to the body-muscles ; it is composed of six pairs of ganglia fused together. The removal of this ganglion occasions [in the Crayfish {Astams fiuvialilis)] the loss of all power of co-ordinated locomotion, PHYSIOLOGICAL SERIES. although other co-ordinated movements of the limbs can still take place. The rest of the ventral-chain ganglia (five thoracic and six abdominal) are transversely con- centrated but longitudinally widely separated. They are situated segmentally, and each gives off a pair of nerves to the appendages of its segment and a second pair to the neighbouring trunk-muscles. In the abdominal region, a third pair of purely motor nerves arise from the connectives behind each ganglion and are distributed to the great abdominal flexor. The terminal ganglion innervates the 6th abdominal segment and the telson ; it also gives off a small rectal nerve, ])robably comparable to the median nerve in the ventral cord of Lepas. The connectives of the ventral chain share in the lateral concentration seen in the ganglia ; in the thorax they lie side by side and (except between the third and fourth ganglia where the sternal artery passes between them) are bound up in a common neurilemma-sheath. In the abdomen they are closely contiguous. The ganglion-cells of the central system are mostly unipolar, and vary much in size, from large pear- shaped cells '2 mm. in diameter to ganglionic nuclei, in which the nucleus is surrounded by a mere film of protoplasm. The latter occur always in masses in connection with certain definite parts of the centx-al system — e.g., the globuli and a restricted area of the suboesophageal ganglion. The nerve-fibres derived from ganglion-cells that lie within the central system are tubular, with a thick neuroglia-sheath (in which myelin may occur) containing a semifluid sub- stance. After leaving the ganglion-cell they give off" a few lateral twigs, that break up in the neuropile and provide a means of communication between the difterent nerve- eleinents. The main fibre then passes either directly into one of the peripheral nerves and is distributed to the muscles, or runs within one of the connectives to a neigh- bouring or distant ganglion and there breaks up in the neuropile. The sensory fibres are very delicate ; they arise, as in Worms, from cells in or close beneath the skin, and enter the ganglia as part of a peripheral nerve. Within the ganglion they divide into anterior and posterior NERVOUS SYSTEM. — INVERTBBRATA. 25 branches, that run in the connectives to neighbouring or distant ganglia. The ganglion-cells cover the lateral and ventral surfaces of the neuropile masses of the ventral-chain ganglia ; the connectives occupy the dorsal surface. In each connective there is a giant nerve-tube ; it originates in a large cell on the ventral surface of the cerebral ganglion and runs the whole length of the chain without apparently giving off lateral branches; it finally divides and passes into the nerves of the tail-fin (uropodites). The giant fibres in their origin and distribution present a striking parallel to Mauthner's fibres in the spinal cord of Fishes, and it has been suggested in both cases that possibly they put the steering and balancing apparatus under the direct control of the brain. In the upper specimen the origin and course of the visceral nerves are seen from the left side, indicated by black paper; in the lower the nervous system is shown, as a whole, in its natural position from above. The left eye has been removed to expose the antennary nerves. 0. C. 1302 I. Krieger, Zeits. wiss. Zool., Bd. xxxiii. p. 55i7 (Anat.). Allen, Quart. Journ. Micr. Sci., vol. xxxvi. 1894, p. 483, & vol. xxxix. 1896, p. 33 {HistoL). Bethe, Arch. f. Phys., Bd.lxviii. 1897, p. 449 [Pliysiol). D. 16. A Lobster {Homarus vulgaris), dissected to show from the ventral aspect the cerebral ganglion and ventral chain. The origins of the optic and antennary nerves are shown, also the divergence of the connectives for the passage of the oesophagus. The degree of transverse approximation of the con- nectives in the region of the thorax has been made apparent by the removal of the common neurilemma-sheath, by which they are naturally bound together. 0. 0. 1301. ITufUerian, D. 16. The cerebral gaugh'on with the eyes and tlu) principal nerves given off from the ganglion, displayed in situ, from II Lohatav {Homarus vulgaris) . O. C. 13U3. Hunterian. 26 rHYblOLOGICAL SERIES. D. 17. Scyllarus arcius, witli the nervous system exposed. The cerebral giinglioa is remarkable for its relatively large size ; it gives oif the usual nerves to the cephalic sense-organs, but the optic tracts and ganglia, owing to the great breadth of the head, are peculiarly long and slender. The sub- oesophageal and thoracic ganglia are longitudinally aj)pproximated, but (with the exception of the componentry of the subcESophageal ganglion) are not fused together. Between the 2nd and ;-5rd and 3rd and 4th thoracic ganglia the connectives are quite separate, leaving in the latter position a large opening between them for the passage of the sternal artery ; elsewhere they are bound together by a common neurilemma-sheath. The last thoracic ganglion is connected with a chain of six segmentally placed abdominal ganglia. They are transversely concentrated, and are connected together by an apparently single cord, the result of the transverse concentration of the paired connectives. Bouvier, Ann. Sci. Nat., ser. 7, t. vii. 1889, p. 73. D. 18. The isolated nervous system of a Hermit Crab {Eupagurus bernhardus). The transverse and longitudinal concen- tration of the components of the suboesophageal-thoracic mass is greater than in Scyllarus, but posterior to the suboesophageal centre the outlines of four gangha can be traced upon the ventral surface of the mass. Three of these are situated in front of the perforation for the sternal artery, and respectively innervate tlie three anterior pairs of thoracic appendages. The fourth centre is formed by the fusion of the last two thoracic ganglia -^vith the first abdominal, it innervates the two posterior pairs of thoracic limbs and the anterior part of the abdomen. The mass is perforated between the 3rd and 4th thoracic ganglia by the sternal artery, and has also two minute openings between the 2nd and 3rd and 1st and 2nd ; beyond the indication afforded by these apertures, all external traces of connectives are lost. The abdominal chain consists of five pairs of transversely concentrated ganglia united by separate connectives. NEKVOUS SYSTEM. — INVHRTEBRATA. 27 D. 19. A Spider-Crab [Muia squinado) dissected from above. The cerebral and oesophageal ganglia, with the nerves that arise from them, are essentially similar to those of the Lobster, except for the great development of the integu- mentary nerves given off from the posterior corners of the cerebral ganglion. The circumcesophageal connectives are remarkably long, owing to the position of the ganglia of the ventral chain. The latter are concentrated to the maximum degree in the longitudinal direction, and are fused together to form an oval mass in the middle of the cephalothorax, from which nerves radiate to the appendages and body. The large appendicular nerves are composed of bundles of small fibres without a common investment. From the dorsal surface of the central mass, at its anterior end, a pair of small nerves are given off to be distributed to the roof of the gill-chamber, and from the posterior end of the mass a bundle of nerves pass into the abdomen. O.C. 1303 A&. Audouin & Milne-Edwards, Ann. Sci. Nat., t. xiv. 1828, p. 92. D. 20. A King- Crab {Limulus polyphemus) dissected from the dorsal aspect. The entire cephalothoracic part of the central nervous system is concentrated around the oral end of the oesophagus in the form of an oval ring. The prge- oral part of the ring represents the cerebral ganglion ; it projects anteriorly as a subcorneal, feebly bilobed mass (protocerebrum) from whose anterior end nerves are given off' to the lateral and median eyes, and to a ventral integu- mentary pit of unknown function situated in front of the mouth. From its dorsal surface, near its union with the lateral parts of the ring, arise a pair of delicate integu- mentary nerves that innervate the ventral skin of the cephalothorax external to the limbs. Between the protocerebrum anu the lateral parts of the ring are a pair of centres (indistinguishable superficially) united by a small prae-oral commissure ; they form part of the cerebral ganglion and give off nerves to the cheliceraj and viscera. The protocerebrum is remarkable for an 28 PHYSIOLOGICAL SERIES. excessive development of a pair of outgrowths similar in many respects to the fmigiform bodies of the Insect- brain (fig. 13). Each of them consists of an arborescent mass of peculiarly dense neuropile coated by a thick layer of ganglionic nuclei ; they cover the whole surface of the protocerebral lobes with the exception of a small area on the dorsal surface. Their function is entirely unknown. Fig. 13. , s N From an enlarged model of the Brain of Limulus, after Viallanes. CH.N. Nerve to clielicerse. F.B. Fungiform body. O.G. Optic ganglion. O.N. Optic nerve. OC.G. Ocellary ganglion. OC.N. Ocellary nerve. P.L. Protocerebral lobe. SN. Nerve to sensory pit. V.N. Visceral nerve. The lateral and posterior parts of the ring are composed of six pairs of ganglionic masses intimately fused together longitudinally and united transversely by a series of com- missures ; the posterior pair are fused in the mid-line to form a single " post-oral " ganglion. Seven pairs of integumentary nerves are given oft from the dorso-lateral margins of the ring, and from its NERVOUS SYSTEM. — INVBRTBBRATA. 29 ventro-lateral border six pairs of pedal nerves, distributed respectively to the five pairs of walking appendages and to the operculum. A pair of fine nerves for the chilaria arise from the ventral surface of the "post-oral" ganghon. The ring is united posteriorly by connectives to a chain of six pairs of transversely concentrated ganglia, situated in the abdomen. From each of these, except the last, two pairs of nerves are given oflp— one to the appendages (gills) of the segment proper to the ganglion, the other to the integument. The latter are united on either side external to the bases of the limbs by a longitudinal con- necting cord, parts of which only are to be seen in the specimen. The three posterior gangha are fused together to form a single nmss, which sends nerves to the last two pairs of gills, the hinder extremity of the abdomen, and the post-anal spine. The central nervous system, together with the motor and some few sensory nerves, is enveloped by a large arterial blood-space; a pair of arteries— branches of the anterior aorta— open into the space on either side above the anterior part of the nerve-ring. Experiments upon this nervous system show that, although parts of it are much concentrated, each segmental centre is entirely inde- pendent in its actions, the regulation and orderly sequence of the movements of different segments being due to the transmission of stimuli from centre to centre, and not to the influence of any one specialized centre of co-ordination. Viallanes, Ann. Sci. Nat., ser. 7, t. xiv. p. 405 {Anat.). Hyde, Journ. Morph., vol. ix. 1894, p. 431 (Physiol.). AEAOHNIDA. St. Remy, Arch. Zool. Exp., t. v bis, 1887, p. 1. 21. The nervous system of a Scorpion {Pandinus imperator), exposed from the dorsal aspect. The main part of the central system lies in the cephalothorax and is concentrated around the oesophagus in a compact mass that represents the cerebral and first nine ventral-chain gangb'a. The cerebral part of the mass is bilobed ; it innervates the median and lateral eyes and the chelicerse. On either side of the oesophagus it is continuous with the anterior region of the 30 PHYSIOLOGICAL SERIES. lavoro oval subcesophageal ganglion — a composite* mass from which nerves are given off to tlu; mouth, the jjedijialpi, the four pairs of walking-logs, and the first four segments of the abdomen. The cephalothoracic mass is united by a })air of delicate connectives to a chain of three abdominal and four post-abdominal ganglia, all of which are trans- versely concentrated but are united by separate connectives. The last abdominal and the first three post-abdominal ganglia lie severally in the segments that they innervate, but the first two free abdominal ganglia are approximated to the cephalothoracic mass, being respectively two segments and one segment in advance of their nerve distribution. The terminal ganglion of the chain lies in the 4th post-abdominal segment ; it supplies the 4th and 5th segments of the post-abdomen and the post-anal spine. The three posterior eanglia and their connectives show a marked increase in size compared with those in front of them, correlated no doubt with the great activity of the post-abdomen. 0. C. 1297 B. Blanchard, L'organisation du R^.gne Animal (Arach- nides), 1852, p. 39. D. 22. A Spider {Avicularia avicularia) dissected from the dorsal aspect. The central nervous system is extremely concen- i rated; it lies in the middle of the cephalothorax behind the mouth, encircling the horizontal part of the oesophagus and extending backwards beneath the stomach. The supra- oesophageal part of the system is small and feebly bilobed ; it innervates the eyes and rostrum. On either side of the oesophagus it is connected to the subcesophageal mass by a pair of ganglionic centres that give off nerves to the chelicerfB and viscera. The third and largest part of the central system lies beneath the oesophagus and stomach, separated from them by the entosternite ; it has an oval form and is composed of six pairs of fused ganglionic centres that represent the ganglia of the ventral chain. From this mass nerves are given off to the pedipalpi, to the four pairs of walking-legs, and to the abdomen. Fibrous partitions, derived from the neurilemma, penetrate to a certain extent between the several centres of the sub- oosophageal mass. O.C.I 300 A. Schimkewitsch, Ann. Sci. Nat., s6r. 6, t. xvii. 1884, p. 15. NERVOUS SYSTEM. — INVERTBBRATA. 3] D. 23. A Pentastomwn tcenioides, in which parts of the nervous system are shown from above (fig. 14). The central system is in a degenerate condition ; it consists of a bilobed ganglionic mass, situated behind the oesophagus. Its lateral parts are united in front of the oesophagus by a delicate commissure, in which there is no sign o£ a prte- oral ganglion. The ganglionic mass gives rise from its posterior surface to a pair of longitudinal nerves of some Fig. 14. C. The Nervous System of Pentastomum tcenioides, after Leuckart. C. Prte-oral commissure. G. Ganglion. L.G. Longitudinal cords. CES. Oilsophagus. size that extend to the hinder part of the body ; it also gives off from its anterior and lateral regions several small nerves to the alimentary canal, body-muscles, and cephalic hooks and papilla;. The specimen shows little beyond the main ganglionic mass. 0. C. 1294 C. Spencer, Quart. Journ. Micr. Sci., vol, xxxiv. 1893^ p. 33. MYEIAPODA. D. 24. Two specimens of the nervous system of a Centipede (^EthmoHtujmus rubripes). The central system shows the Arthropod typo in a very simple condition ; it consists of PHYSIOLOGICAL SERIES. a bilobed cerebral ganglion of relatively uncomplicated structure, and of a chain of 22 transversely concentrated post-oral ganglia, united to one another by transversely separate connectives. The cerebral ganglion (fig. 15) is composed of two pyriform lobes on either side, situated one above the other with their long axes at right angles. The dorsal pair are set transversely to the axis of the body, and give off from their pointed outer ends a bundle of optic nerves. The ventral pair innervate the antenntG ; they lie slightly in advance of the dorsal lobes Fig. 15. The Brain of Scolopendra morsitans, after St. Remy (Ventral aspect). A.L. Antennary lobes. O.L. Optic lobes. V.N. Visceral nerves. with their axes longitudinal. In front they are continued into the antennary nerves, and behind into the circum- oesophageal connectives. Glomerulated condensations occur in their neuropile similar to those found in the antennary lobes of other Arthropods, and from their posterior parts nerves are given off to the viscera. The suboesophageal ganglion is larger than the rest of those in the ventral chain ; it innervates the jaws and other mouth appendages. The succeeding 21 ganglia are similar to one another. They are arranged segmentally, and each gives off four pairs of nerves — one to the limbs and the rest to the body- wall and trachea3 of the same segment. NERVOUS SYSTEM. — INVERTEBRATA. 33 In the lower specimen the nervous system has been ex- posed from the dorsal aspect, the isolated anterior part of another being mounted above. D. 25, A Centipede {Scolopendra mo7'sitans) with the integument and muscles removed from the right side so as to give a lateral view of the nervous system. The Huntex'ian de- scription of this specimen is as follows : — " Centipede — the brain a small roundish body laid bare : the two great nerves going to the tail with ganglions at the places where they give off nerves, as in the Lobster." The part above alluded to as the brain is the large suboesophageal ganglion ; the union o£ the connectives above the cesophagus is not shown. The ventral position of the ganglia and the nerves given off from them are well displayed in this preparation. 0. C. 1298. Hunterian. D. 26. The isolated nervous system of a Centipede {Scolopendra sp.). Preserved in Goadby solution. INSEOTA. Viallanes, Ann. des Sci. Nat., ser. 7, t. xiv. p. 429. Binetj Jour, de I'Anat., t. xxx. 1894, p. 449. Brandt, Horae Soc. Entom. Ross., t. xv. 1879, p. 2. In the Insecta, apart from the complexity of the cerebral ganglion, one of the most noteworthy features is the variable degree of longitudinal concentration of the ganglia of the ventral chain, either when comparison is made between adults of different species or between the larva and imago of the same species. As a rule the nervous system of the adult is more concentrated than that of the larva. Concentration usually appears first amongst the abdominal ganglia, resulting in the fusion of some at the posterior end of the chain and the in- clusion of some in front in the metathoracic ganglion. The thoracic ganglia also fuse in various ways, though less fre- quently. The pro- and mesothoracic, meso- and metathoracic, or all three, may thus unite. Although in some Orders (e. ^. Lepidoptera) a certain definite arrangement of the ganglia is fairly constant, in most it is not VOL. II. D 34 PHYSIOLOGICAL SERIES. SO, and a variety of stages o£ concentration occur within the Order. In the embryo the nervous system is usually entirely unconcentratedj and the adult condition is attained by the suc- cessive fusion of ganglia in the embryonic and pupal stages. Some embryos, however, have a single unsegmented post-oral mass, from which the ganglia of the adult are produced by subsequent segmentation. D. 27. Models of the brain (cerebral ganglion) and right fungi- form body of a Black-beetle {Pei'ijjlaneta orientalis) x 60, with a drawing of a transverse section through the left half of the ganglion, the position of which is indicated by a black line on the model. The cerebral ganglion in Insects consists to a large extent of a pair of proto- cerebral lobes in connection with the optic ganglia ; thus the size of the brain depends mainly upon the degree of development of the eyes, and need not necessarily afford an indication of the state of intelligence of the individual. The brain further comprises a second pair of centres (deutocerebrum) , probably olfactory, in connection with the antennaa; and a third pair (trito- cerebrum), situated in the roots of the circumoesophageal connectives, that innervates the labium and gives rise to the visceral system. It apparently corresponds to the oesophageal ganglia of Crustaceans. The protocerebrum consists" of the optic ganglia (not shown in the model) and of a pair of large protocerebral lobes, contiguous in the mid-line. The latter are united by commissures, and each contains several remarkable struc- tures. The most striking of these are the fungiform bodies — organs that are possibly indicated in Crustacea, but reach their full and characteristic development in Insects. One is lodged in each protocerebral lobe ; it consists of two masses of dense neuropile (calyces, F) deeply concave from side to side, and situated near the dorsal surface of the brain with their concavities facing upwards. (The calyces are exposed on the right side of the model.) Their neuropile derives its fibres from a cap of ganglionic nuclei (coloured yellow). Each calyx gives off from its lower (convex) surface a short pedicle, that unites with its fellow NERVOUS SYSTEM. — INVBRTEBRATA. 35 to form a common neuropile-stalk (peduncle, Gr). This stalk penetrates directly downwards through the substance of the protocerebral lobe till it reaches the mid-horizontal plane of the brain. Here it gives off two branches, one of which (cauliculus, H) curves forward and upward near the anterior surface of the brain to terminate in a rounded end close beneath the anterior lip of the outer calyx ; the other (trabecula, I) runs diagonally downwards and inwards, till it meets its fellow, without fusion, in the mid-line. The fungiform bodies do not directly give rise to any nerves, but they enter into close relations with all parts of the brain by means of fibrous tracts, the most important of which pass to the optic ganglion of the same side, to the opposite fungiform body, to the corpus centrale, and to the antennary lobe of the opposite side. Fibres belonging to this latter tract continue directly past the fungiform body into the optic ganglion, and constitute an optico-olfactory chiasma similar to that seen in Decapod Crustacea. In spite of the evident importance of these structures their function is still unknown, but it is noteworthy that within the same Order their size increases roughly in pro- portion to the intelligence of the Insect, and among social forms they may even vary in development between the persons of the society — being, for instance, proportionately larger in the Worker bee than in the Drone or Queen. The protocerebral lobes are united across the mid- line by two bands of deeply staining neuropile. One of these (the pons) lies immediately below the dorsal point of union of the two halves of the brain ; it is in the form of a for- wardly directed horseshoe, and stands in close relation to the roots of the nerves to the white spots (vestigeal ocelli). A similar though backwardly directed horseshoe-shaped band gives origin to the ocellary nerves in Limulus, and there is a somewhat similar strand in the fore part of the brain in Decapod Crustacea. The second commissural band (corpus centrale) is larger and o£ more complicated structure ; it has the form of a crescentic plate hollowed below, and consists of two layers of neuropile. It lies approximately in the centre of the D 2 36 PHYSIOLOGICAL SERIES. brain, and apparently forms a nucleus to which fibres from all parts converfre. The most important tracts in con- nection with it are derived from the fungiform bodies and optic and antennary lobes ; beneath it lie a pair of small neuropile masses — the tubercles of the corpus centrale (The corpus centrale and tubercles are shown in the drawing directly above the trabecula.) A similar though simj)ler median band lies between the protocerebral lobes in the Decapod Crustacea. The antennary lobes (deutocerebrum) consist of two lobules on either side united by transverse commissures ; the ventral of the two gives oflF the larger part of the antennary nerve (probably olfactory) ; its neuropile is glomerulated. A second smaller root of the antennary nerve is derived from the dorsal lobule, it is chiefly motor in function. A small tegumentary nerve rises from the anterior face of the ventral lobule. Each half of the tritocerebrum gives off a nerve from its anterior surface that meets its fellow in tlie mid-line to form a triangular ganglion (frontal ganglion, E) from which a median nerve runs back along the alimentary canal. These models, which were cast from originals recon- structed from a series of transverse sections by Mr. E. T. Newton, have been diagrammatically painted and have certain parts and areas indicated by letters and numbers, the key to which is mounted below the models. Newton, Quart. Journ. Micr. Sci., vol. xix. 1879, p. 340. .D. 28. Two specimens of a Cockroach [Blatta americana) dis- sected to show the nervous system from the dorsal and ventral aspects. The dorsal surface is shown in the loft-hand specimen, the ventral in the right. The cerebral ganglion lies in the head, and is so placed that the optic lobes lie vertically above the antennary. The suboesophageal ganglion for the innervation of the mouth-parts is also situated in the head close below the cerebral j it is united by a pair of connectives to a ventral chain composed of 9 paired ganglia. The anterior three are. larger than the rest, and lie one in each thoracic segment at equal distances NERVOUS SYSTEM. — IN VERT EB RATA. 37 apart. Each gives off uerves (seen best in the right-hand specimen) to the legs and body muscles, and (in the case of the posterior two) to the wings. In the abdomen the ganglia of the chain are situated at irregular intervals — the first four fairly close together, the last three somewhat further apart. The terminal ganglion (6tb) is larger than the rest and represents a fusion of the two posterior larval ganglia ; it innervates the hinder end of the body, the rectum, the genital organs, and the cerci. Each of the other abdominal ganglia gives oflF a single pair of nerves to the body-walls and trachese. The ventral-chain ganglia are composed of definite dorsal and ventral masses of neuropile, from which the nerves arise by two or more independent roots, that appa- rently convey either motor or sensory impulses according as they spring from the dorsal or ventral mass. The pro- bability of a localisation of motor and sensory functions in opposite regions of the cord of Arthropods has been dis- cussed since the idea was brought forward by Newport. Later observations have tended to show that in the case of Crustacea such localisation does not occur, but that in Insects it most probably does. This latter con- clusion rests not only upon physiological experiments, but is also based upon anatomical grounds — more particularly upon a comparison of the alar nerve-roots in flying beetles with those of beetles whose wing-cases are present but immoveable. In the former case each alar nerve rises by two main roots, one from the dorsal mass of neuropile, the other from the ventral. In the beetles with purely pro- tective non-motile wing-cases (e. g. Blaps mortisaga) the dorsal root is entirely absent (Binet, I.e.). Preserved in Goadby solution. Miall & Denny, Life History and Structure of the Cockroach {Periplaneta orientalis), 1886, p. 86. D. 29. A large female Ortho])terous Insect (Karahidion anstrale) with the nervous system shown from the dorsal aspect. The thoracic ganglia are nearly equal in size, and lie, widely separated, in the three thoracic segments. There are six free abdominal ganglia, situated respectively in 38 PHYSIOLOGICAL SERIES. successive abdomintal segments from the 2nd to the 7th. Each of the anterior five innervates the segment in which it lies ; the 6th gives off nerves to the hinder end of the body. The 1st abdominal segment is supplied by the metathoracic oanglion. 0. C. 1299 e. D. 30. A Locust {Tropidacris latreillei) dissected from the dorsal aspect. The cerebral ganglion is small compared with the size of the head, and is united to the suboesophagpal ganglion by relatively long connectives. The three thoracic ganglia are separate, although the meso- and metathoracic show a certain amount of approximation. The metathoracic ganglion is much larger than the other two ; it sends a number o£ nerves to the anterior parts of the abdomen in addition to those to the metathorax, and probably repre- sents a fusion of the true metathoracic ganglion with a certain number of abdominal ganglia. Within the abdomen there is a chain composed of five separate ganglia situated respectively in the 2nd, 4th, 6th, 7th, and 8th segments. The first of them innervates the fourth segment ; the last is larger than the others and is no doubt a compound mass. 0. C. 1299 c. D. 31. A female Stick-insect {Pseudohactena ?) showing the nervous system from the dorsal aspect. The entire system is of the most delicate nature and, in conformity with the general structure of the insect, is greatly extended longi- tudinally. The cerebral and suboesophageal ganglia are not visible. The three thoracic ganglia are separate ; they are followed by a chain of five abdominal ganglia situated respectively in the 2nd to the 6th abdominal segments. The first of these free ganglia innervates the 2nd segment of the abdomen, so that presumably the first primitive abdominal ganglion is included in the meta- thoracic. The t(!rminal ganglion innervates the posterior region of the body and the genitalia. The genital organs are also shown in this specimen. 0. C. 1299 D. Miiller, Nov. Act. Nat. Curios., Bd. xii. 1825, p. 568. NERVOUS SYSTEM . — INVERTEBRATA . 39 D. 33. All immature Water- Scorpion (Belostoma) showing the nervous system. In all the Hemiptera the post-oral part of the central nervous system shows a high degree o£ longitudinal concentration, and in none perhaps more so than in the Water-Scorpions. In this example the sub- oesophageal ganglion lies close to the cerebral, in the pro- thorax ; it is almost contiguous with the prothoracic ganglion, the approximation o£ the two being evidently due to the forward position of the 1st pair of legs. The meso- and metathoracic ganglia are fused with one another and with the abdominal chain to form a round central thoracic mass from which nerves are given off to the two posterior pair of thoracic limbs and to the abdomen. Owing to the half-macerated condition of the specimen, the component parts of the central thoracic mass are visible as three pairs of opaque centres representing respectively the meso- and metathoracic ganglia and the united ganglia of the abdominal chain. 0. C. 1299 B. D. 33. Two specimens of the nervous system of another species of Water-Scorpion [Nepa cinerea). In its main features this system corresponds with that shown in the last speci- men, but the longitudinal concentration is even more marked. In this species the suboesophageal ganglion is completely fused with the prothoracic. In the upper specimen the nervous system is seen isolated ; in the lower in situ. 0. C. 1299 B a. D. 34. The nervous system of a Lepidopterous larva exposed from the dorsal aspect. The cerebral ganglion consists of two small rounded lobes contiguous in the mid-line. It is united around the oesophagus by a pair of short connectives to a ventral chain, composed (as in the great majority of Lepidopterous larvte) of 11 equal-sized ganglia — i, e., 1 suboesophageal, 3 'thoracic, and 7 abdominal. The sub- cxisophageal and prothoracic ganglia are approximated to one another ; but the remainder lie at about equal distances apart in successive segments of the body. The terminal ganglion is distinctly grooved transversely and represents a fusion of two embryonic ganglia. As in the adult, it 40 PHYSIOLOGICAL SERIES. innervates the reproductive organs in addition to the hinder region o£ the body- wall. The connectives of the ventral chain are very slender ; they lie close side by side, except between the three thoracic ganglia where they are trans- versely separated. 0. C. 1299 G. D. 35. The larva o£ a Moth [Metura saundersii) contained within its protective case and dissected from the ventral surface. The nervous system is of extreme delicacy. It does not differ in the number of its post-oral ganglia from that shown in the preceding specimen, but the altered positions of the ganglia relative to the body-segments and to one another suggest that those changes have begun, which finally^ during the pupal stage, produce the longitudinal concentration of the nervous system found in the imago. The first abdominal ganglion is for example markedly approximated to the metathoracic, and lies with it in the metathoracic segment. 0. C. 1299 f, D. 36. Two specimens of the nervous system of the larva of a Goat Moth (Cossus ligniperda) : one in situ seen from above, the other isolated. The cerebral and suboesophageal ganglia are moderately separate, but the prothoracic is almost confluent with the suboesophageal. It is followed by a chain of 10 ganglia (2 thoracic and 8 abdominal). Between the thoracic ganglia the connectives diverge laterally, leaving an oval space. In the anterior of these spaces, in the left specimen, a small median nerve can be seen, which arises from the prothoracic ganglion and ends in two lateral branches close in front of the mesothoracic. It belongs to a series of median sympathetic nerves, found commonly among insects ; as a rule each rises from one of the two connectives close behind a ganglion, or from the ganglion itself, runs to the succeeding ganglion and there divides into two lateral branches, each of which joins one of the peripheral nerves and is distributed to the respiratory organs. The abdominal ganglia are situated at equal distances apart, with the exception of the first which is a})proximated to the metathoracic, and the last two which are almost contiguous. Cattie, Zcits. wiss. Zool., Bd. xxxv. 1881, p. 304. NERVOUS SYSTEM. — INVERTEBRATA. 41 r. 37. A Lainellicorn Beetle (Dynastes centaurus) dissected from above to show the nervous system. The cerebral ganglion is comparatively small ; it is united to the suboesophageal by connectives of moderate length. In the thorax there are three ganglionic masses, o£ which the anterior two are simple and respectively constitute the pro- and meso- thoracic ganglia ; the posterior mass is elongated in shape, and consists o£ the true metathoracic ganglion fused with a short cylindrical appendage that represents a concentra- tion of the abdominal chain ganglia, and innervates the abdomen. This arrangement of the ganglia is the one usually found among Lamellicorns. D. 38. A male Longicorn Beetle (Macrotoma) showing the nervous system from above. The cerebral ganglion is small relative to the head, and is united to the suboesopha- geal ganglion by long connectives. The thoracic ganglia are separate, with approximation between the meso- and metathoracic. The latter innervates the anterior part of the abdomen, as well as the metathorax. There are four free abdominal ganglia, the first of which is situated on the boundary-line between the thorax and the abdomen. This number and arrangement of the ganglia is charac- teristic of this family of Beetles. 0. C. 1299 A. D. 39. The nervous system of a Hornet (Vespa crahro), isolated. The large size of the cerebral ganglion is due, partly to the bulk of the protocerebral lobes — the centres for the great compound eyes, and partly to the high degree of develop- ment of the fungiform bodies. The latter differ in many respects from those of the Black-beetle (D 27); their calyces are larger and arch to a considerable extent over the anterior and posterior surfaces of the proto- cerebral lobes ; the peduncle and its two calycal branches are remarkably stout, but the caidiculus and trabecula are insignificant, and without definite outlines. The ocelli receive their nerves from three centres that lie directly beneath them. The cerebral ganglion is continuous around the oesophagus with the small suboesophageal ganglion.. There arc two ganglia in the thorax— the first is the pro- 42 PHYSIOLOGICAL SERIES. thoracic, the second ca compound muss that represents a fusion of the meso- and metathoracic ganglia with the first two abdominal. In the abdomen there are five separate ganglia, the last of which is double and is formed by the fusion of two larval ganglia. Viallanes, Ann. Sci. Nat., ser. 7, t. ii. 1887, p. 1 MOLLUSCA. V. Ihering, Anat. des Nervensystemes . . . . der Mollusken, 1877. Garstang, ' Science Progress,' vol. v. 1896, p. 38. The central nervous system of the Mollusca may be compared with that of an Annelid or Arthropod in so far as it is essenti- ally bilaterally symmetrical and consists of a paired prae-oral centre united around the oesophagus to a ventral system below the gut. But in Molluscs the ventral system, when longitudinally elongated, shows no true metameric segmentation, and thus differs fundamentally from the ventral chain system of Annelids and Arthropods, although it much resembles the ventral cords of a Turbellarian. In addition to the prte- and postoral centres common to most Invertebrates, there are present others peculiar to the Mollusca. The most important of these are certain pallio-visceral centres for the innervation of the mantle, gills, and parts of the viscera. They occur either as a simple ganglionic loop uniting the lateral parts of the circum-oral system, or as a number of isolated ganglia (pleural, branchial, abdominal) united together by a fibrous commissure and due apparently to the disintegration of some such generalised loop. Modification in the various groups of Molluscs tends either towards the concentration of all the centres towards the head (Gastropods, Cephalopods), or— in the Pelecy pods— towards the diminution and suppression of the cerebral and pedal ganglia owing respect- ively to the absence of the head with its sense-organs and to the degeneration in many forms of the foot or byssal apparatus. Besides this reduction of the anterior ganglia, thei'e is, in the Pelecypods, a backward migration of the pallio-branchial centres (visceral ganglia) and a progressive increase in their size, lateral NERVOUS SYSTEM. — INVERTBBRATA. 43 concentration, and complexity of structure, depending upon the perfection of the mantle sense-organs or the formation of siphons. PBLECYPODA. Rawitz, Jena. Zeits., Bd. xx. 1887, p. 384. D. 40. A wax model of the nervous system of Nucula nucleus, X 25. The central system, as in other Pelecypods, consists of three pairs of ganglia united to one another by com- missures and connectives. The cerebral ganglia lie in front of the mouth united by a short commissure ; each gives off three nerves that respectively innervate the anterior adductor, labial palps, and anterior part of the mantle. Posteriorly, the cerebral ganglia gradually di- minish in thickness and pass insensibly into a pair of long cerebro-visceral connectives, by which they are united to the visceral ganglia. The latter are small and laterally separate ; they lie ventral to the gut at some little distance in front of the posterior adductor united by a definite commissure, and innervate the gills, posterior adductor, and posterior part of the mantle. The cerebro-pedal connectives arise from the inner ventral surface of each cerebral ganglion by two roots, that remain separate for a fourth of the distance to the pedal ganghon. The double origin of these connectives from each cerebral ganglion has been thought to indicate that the latter is a compound structure consisting of two ganglia comparable to the cerebral and pleural of the Gastropod. But it may be, that the posterior root of the cerebro-pedal connective is the proximal part of the otocystic nerve running free for the first part of its course and not completely united with the cerebro-pedal connective as in most other Pelecypods. It is suggestive in this connection that in Solenomya (another of the Protobranchia) the otocystic nerve is entirely free from cerebral ganglion to otocyst. The pedal ganglia lie in the substance of the foot closely united together by a double commissure; they innervate the pedal muscles. The nervous system shows its low organisation by the diffuse distribution of ganglion-cells upon its surface (indicated by 44 PHYSIOLOGICAL SERIES. yellow in the .specimen). They not only liorni a layer of .some thickness iii)on the three pairs o£ ganglia and the root o£ the branchial nerve as in other Pelecypods, but cover the outer and dorsal surfaces of the cerebro-visceral connectives and the cerebral and visceral commissures. Pelseneer, Arch, de Biol., t. xi. 1891, p. 16G. Drew, Quart. Journ. Micro. Soc, vol. xliv. 1901, p. 373. D. 41. The nervous system of an Edible Mussel {Mytilus edulu), isolated. The ganglia are small — the pedal and visceral of approximately equal size, the cerebral slightly smaller. The latter lie on either side of the mouth, united by a long prseoral commissure. From the posterior extremity of (uich a single cord is given off, which shortly divides to Ibrm the cerebro-pedal and cerebro-visceral connectives. The pedal ganglia lie between the viscera and the foot ; they are closely applied to one another, and each gives off two main nerves — a large one from its lateral border to the pedal muscles, and a smaller posterior one to the byssus gland. The visceral ganglia lie some distance apart upon the autero-ventral surface of the posterior adductor, united to one another by a slightly ganglionic commissure. Each ganglion gives off two principal nerves, an anterior ganglionic branchial nerve and a large posterior trunk that supplies the mantle and posterior adductor. D. 42. Two specimens of the nervous system of a Scalloi) [Pecten maximus) — one isolated, the other shown within the body from the left side. The remarkable perfection of the sense-organs on the mantle-border of the Scallops, and the large size and energy of their adductor muscle, are accompanied by a corresponding development of the visceral ganglia, the centres from which these parts are mainly innervated. The ganglia are completely fused in the mid-line, and form a rectangular mass situated upon the ventral surface of the adductor, near the centre of the animal. Each anterior corner receives one of the cerebro-visceral connectives ; external to these arise the branchial nerves, followed, along each lateral margin of the ganglion, by a series of lateral mantle-nerves, distributed to the middle NERVOUS SYSTEM. — INVBRTEBRATA. 45 region of the mantle-border. From each posterior corner arises another bundle o£ nerves (posterior pallial), which innervates the posterior adductor and the hinder sixth of the mantle-border. The branches o£ the pallial nerves just before their final distribution are united by a ganglionic cord (not shown in the specimen) that runs completely round the mantle parallel to its edge. The cerebro-visceral connectives lie for their posterior third upon the surface of the adductor ; antei'ior to that point they travei-se the superficial parts of the gonad to reach the small cerebral ganglia. The latter lie behind the mouth, united prseorally by a very long and delicate commissure; they give off nerves to the anterior part of the mantle and labial palps. The pedal ganglia are small and contiguous in the mid-line ; they lie above the foot, between the cerebral ganglia. 0. C. 1303 E h. D. 43. Two specimens of the nervous system of a Pond-Mussel [Anodonta cygnea), shown respectively from the left side in situ, and isolated. The ganglia are more marked than in Mytilus, but show much the same relative proportions to one another. The cerebral lie at the postero-lateral margins of the mouth, and are united prseorally by a long commissure ; each gives off the usual nerves to the mantle, palps, and anterior adductor. The pedal ganglia are closely applied to one another, and are situated in the upper part of the foot embedded in the viscera ; they give off numerous nerves to the pedal muscles and integument. The cerebro-visceral connectives run one on either side of the body on a level with the line of attachment of the gills; at their anterior end they lie far apart near the surface of the visceral mass, but towards the visceral ganglion run close together, between the organs of Bojanus. The visceral ganglia are larger than either cerebral or pedal ; they are fused together to form a bilobed mass situated on the ventral surface of the posterior adductor. They give off several small visceral filaments from their anterior surface, and two pairs of larger nerves from their lateral and posterior borders. The lateral pair supply the gills, and have at their origin a ganglionic area that underlies a 46 PHYSIOLOGICAL SERIES. special branchial sense-organ (osphradium). The posterior nerves are distributed to the mantle (particularly to the papillae that surround the inhalent opening) and to the posterior adductor. In the lower specimen black paper has been placed beneath the ganglia. 0. C. 13();5 e a. AMPHINEUEA. Plate, Zool. Jahrb., Suppl.-Bd. iv. 1898, p. 151. D. 44. The central nervous system of a Chiton {Ilanleya ahyssorum), showing some of its more important features. The nervous system in this and other Amphineura consists fundamentally of two pairs of longitudinal cords united anteriorly to a circumoral ring. An even layer of ganglion- cells covers all parts of the cords and ring, without local concentration to form special ganglia, except in the Aplacophora and one species of Chiton. The outermost pair of cords (lateral cords) lie in the body-walls above the branchial furrow, lodged between the main branchial vessels ; they innervate the mantle with its sense-organs, and, from their slightly thickened posterior fourth, the gills and probably also the renal organs and heart. They are continuous with another above the rectum, and thus form an elongated loop, comparable, apart from its relation to the rectum, to the visceral loop of Gastropods and Pelecypods. The ventral or pedal cords extend throughout nearly the whole length of the foot, buried in its substance. They are united together by a large number of very delicate and somewhat irregularly disposed commissures, and give off from their outer and ventral surfaces numerous pedal nerves, that unite to form a rich plexus in the muscles of the foot. The first and last of the series of pedal commissures are far stouter than the rest, (in the specimen these two are perfect, the roots only of the other commissures and of the pedal nerves are shown). The pedal and lateral cords of the same side unite together in front to form the band- like anterior part of the circumoral ring. Behind the mouth the ring is completed by a slender strand, that terminates on either side in a swelling at the anterior end NERVOUS SYSTEM. — INVERTEBRATA. 47 of the pedal cord. From these swellings, which much resemble the labial lobes of Haliotis, two pairs of con- nectives are given off — one to the gangha of the subradular organ (imperfect in the specimen), the other to the buccal ganglia, which lie as usual upon the posterior surface of the buccal mass, between the oesophagus and radular sac. The buccal system in this and certain other species forms a second complete ring around the gut : the buccal ganglia being united by commissures both below the oesophagus and above the roof of the buccal mass. The buccal ganglia probably innervate the whole alimentary canal. 0. C. 1305 c. Burne, Proc. Make. Soc, vol. ii. 1896, p. 4. D. 45. The anterior part of the nervous system of the same species of Chiton, isolated to show the two nervous rings (circumoral and buccal) that surround the alimentary canal. 0. C. 1305 I). GASTEOPODA. Bouvier, Ann. Sci. Nat., ser. 7, t. iii. 1887, p. 1. D. 46. An isolated specimen of the nervous system of an Ormer (^Haliotis tuherculata) . The cerebral ganglia are small but fairly distinct, and are united in front of the mouth by a long ribbon-like commissure. From the lateral parts of each, two connectives pass beside the buccal mass to a compound pleuro-pedal ganglion beneath the gut. The greater part of this ganglion belongs to the pedal system, and extends backwards in the substance of the foot as a pair of flattened cords, fused to one another and to the pleural centres at their anterior end, and united at intervals by nine transverse commissures. Nerves are given off from this " ladder-like " pedal system to the foot and epipodium. The pleural ganglia form a pair of indefinite excrescences on the dorsal surface of the fused anterior ends of the pedal cords. They give off a pair of large mantle-nerves, and are united together, as in other Prosobranchs, by a commissural loop (visceral loop), that in its passage from ganglion to ganglion is twisted in the form of an 8. This twisted or streptoneurous loop is characteristic of the Prosobranchs, 48 PHYSIOLOGICAL SERIES. and always bears in its HifFercnt, parts a dcfinito relation to the gut. The arm of the visceral loop that rises from the left pleural ganglion passes beneath the gut to the opposit(! side of the body ; here, at a point slightly posterior to the free tip of the gill, it forms a ganglion (subintestinal ganglion) from which the gill and olfactory organ (osphr.i- (lium) are innervated. The loop continues its course round the margin of the mantle -cavity, and at its hindermost extremity forms another ganglion (abdominal ganglion), from which several nerves are given off to the viscera. On the left side of the mantle-cavity, opposite the sub- intestinal ganglion, a third ganglion (supraintestinal) is formed for the innervation of the left gill and osphradiuin. After leaving this ganglion the loop turns to the right over the dorsal surface of the intestine, and finally enters the right pleural ganglion. Nerves are given off from the cerebral ganglia to the sense-organs and integument of the head ; those to the lips take their origin, in common with the buccal connectives, from a prominence on the antero-ventral surface of each ganglion (labial lobe). The buccal ganglia form a single horseshoe-shaped band, situated on the posterior wall of the buccal mass between the radnlar sac and oesophagus. 0.0. 1305 F. Lacaze-Duthiers, Ann. Sci. Nat., ser. 4, t. xii. 185il, p. 247. D. 47. The nervous system of a Limpet {Patella vulgata\ isolated. This nervous system agrees in its general features with that of Ilaliotis, but differs from it in the following important particulars : — The ganglia are more pronounced and independent : this difference is particularly marked in the separation of the pleural and pedal ganglia. The pedal cords are not fused at their anterior end, but form a pair of ganglionic enlargements united by a stout commissure. Posteriorly they gradually become purely fibrous. The jiedal cords are united by two commissures only. The labial lobes are detached from the cerebral ganglia. A nerve of some length is interposed between the sub- and supraintestinal ganglia and the visceral loop. 0. 0. 1305 E. NERVOUS SYSTEM, — INVEllTEBKATA. 49 48. The nervous system of an Apple- Snail {Amjoullaria urceus), isolated excepting the pedal nerves of the right side. The nervous system of this Prosobranch affords a strikino- example of a condition of the visceral loop, known as zygoneury ; by this is meant the presence of certain con- nections between the sub- and supra-intestinal ganglia and the pleural gangHon of the same side, whereby a kind of false orthoneury arises that to a greater or less extent masks the original streptoneurous condition of the loop. These connections occur commonly among Prosobranchs and can be present on one or both sides constituting right, left, or double zygoneury according as the nervous union takes place between the right pleural and subintestinal ganglia, the left pleural and supra-intestinal, or both. In this specimen double zygoneury is shown in an extreme form. The visceral loop passes from the left pleural ganglion beneath the intestine to a small subintestinal ganglion partially fused to the right pleural ganglion— this zygoneurous connection. From the subintestinal ganglion the visceral loop runs round the margin of the mantle-cavity as usual, giving off a nerve to the mantle on the right side and several to the viscera from a bilobed abdominal ganglion situated at its posterior ex- tremity. The left arm of the loop, after giving off' a few small nerves, enters an elongated supra-intestinal ganglion, which gives origin to a stout nerve for the osphradium and several smaller branches that are said to pass across the roof of the mantle-cavity to the gill, which in this mollusc is displaced from the left to the right side by the development of the lung-sac. The supra-intestinal ganglion is connected by a large trunk to the left pleural ganglion (the left zygoneurous connection) and to the right pleural ganglion by a delicate filament that passes dorsal to the intestine and subintestinal ganglion, and represents the supra-intestinal arm of the streptoneurous loop in a very much reduced condition. The pleural ganglia are fused to the pedal to form a pair of subcBsophageal masses, in each of which the constituent parts are separated by a shallow depression. They are connected by three commissures — one between the pleural VOL. II. PHYSIOLOGICAL SERIES. centres, the other two between the pedal. The nerves from the pleural ganglia innervate the mantle ; one of those on the right side is of large size, and forms a considerable ganglion before breaking up to innervate the penis, rectum, and neighbouring parts. The pedal ganglia are continued backwards in the substance of the foot as a pair of longi- tudinal /??;7*o?<5 cords, connected together by .3 or 4 delicate commissures. From their outer sides a number of pedal nerves are given off, which towards the margin of the foot form a rich plexus with minute ganglia at the meeting- points of the nerve-filaments. The pedal system, except for the absence of ganglion-cells in the longitudinal cords, closely resembles the " ladder-like " system of Vivipara [Paludina], The cerebral ganglia are united by a long ribbon-like commissure; they innervate the cephalic sense- organs, and are united by a pair of long connectives to two small buccal ganglia situated in the usual place on the posterior surface of the buccal mass and connected by a suboesophageal commissure. 0. 0. 1305 G. Burne, Proc. Malac. Soc, vol. iii. 1899, p. 317. 49. A Heteropod (Carmaria mediterranea) with the nervous system displayed from the left side. The system, which is very delicate compared with the size of the animal, bears many resemblances to that of a Prosobranch. particularly in the possession of a crossed (streptoneurous) visceral loop. The ganglia are considerably lobulated. There are two main pairs — (i.) the cerebral (fig. 16), from which nerves are given off to the large and highly-organised eyes, the otocyst, tentacles, and labial region of the integument ; and (ii.) the pedal ganglia. The latter lie above the fin within the body ; each is bilobed, with the two lobes one above and slightly in front of the other. The upper lobe receives a stout connective from the cerebral ganglion, and gives off from its hinder end a connective to the visceral ganglion of the same side, and from its upper surface 3 or 4 fine nerves that radiate to the body- wall. A large nerve for the penis rises from the upper lobe on the right side. The lower lobe sends nerves to the body-wall and to the various regions of the foot, that to the fin being NERVOUS SYSTEM. — INVBRTEBRATA. 51 particularly large. A pair of long slender connectives arise from a lobe (fig. 16, pl.l.) on the posterior surface of each cerebral ganglion and accompany the alimentary canal ; near the visceral mass each crosses to the opposite side of the body— the left below the gut and the right above, and upon reaching the visceral mass is joined by the above-mentioned pedo-visceral connective, and swells to form^ a small visceral ganglion upon the surface of the gastric gland. These two visceral ganglia represent the Fi^. 16. PL'V. C. C.P. C. Cerebral Ganglia of Carinaria tnediterranea. C.P.C. Cerebro-pedal connective. O.N. Optic nerve. PL.L. Pleural lobe. PL.V.C. Pleuro-visceral connective. supra, and subintestinal of a Prosobranch ; each is united by a delicate filament to a large abdominal gano-lion situated upon the gastric gland midway between the'two The gill IS innervated from the supra-intestinal ganglion Ganglia comparable to the pleural of other Gasteropods are not present as independent centres ; they are probably fused with the cerebral ganglia, forming the lobes from which the visceral loop arises. Pelseneer, C. R. Acad. Sci., t. cxiv. 1892, p. 775. D. 50. Two specimens of the nervous system of a Roman Snail {Helix pomatia), shown respectively in situ from the left side, and isolated. The central system is much concentrated. It consists of two main ganglionic masses— (i.) a paired oblong cerebral ganglion, united by two connectives on either side of the B 2 52 rHYRIOLOGICAL SERIES. oesophagus to (ii.) a laroe compound suboesophageal mass formed by the fusion of ])edal and pleural ganglia witli the four centres of the short untwisted (orthoneurous) visceral loop. The two halves of the cerel)ral ganglion are united by a short commissure ; each is indistinctly lobulated, the most conspicuous lobe, forming a conical projection (tentacular Fig. 17. P. G. i Diagrammatic reconstruction of the Pleui'o-pedal mass of Helix jmnafia. X 20. C.P.C. Cerebro-pedal connective. C.PL.U. Cerebro-pleural connective. P.O. Pedal ganglion. PL.G. Pleural ganglion. Y.L. Visceral loop. lobe) on its anterior surface, from which arises a large nerve for the optic tentacle and eye aud a smaller one for the otocyst. From the antero-lateral margins of the ganglion, nerves are given off to the lips and anterior tentacles, and from its ventral surface a pair of delicate buccal connectives. The substance of the suboesophageal mass (fig. 17) is traver.sed between the pleuro-visceral and pedal centres by the anterior aorta. The pleural ganglia give off no nerves. Four large nerves rise from the ganglia of the visceral loop ; three of tliem innervate NERVOUS SYSTEM. — INVERTEBRATA. 53 the mantle and respiratory organs, the fourth enters the visceral mass and is distributed to the genital organs. The pedal ganglia are united by two distinct commissures ; each aives off a large bundle of nerves to the foot. The entire central system is enclosed in a thick sheath of connective tissue (fig. 18). There are two distinct kinds of ganglion-cells — large unipolar cells, some of immense size {'ll mm.) situated around the suboesophageal and Fig. 18. . .T.L C.T. ^11^; G.n. 'Mm ''■''^' ..■mm '>:■■- ^•^'-•■^^^^^^^■^ ^ Horizontal section tlirougli the right Cerebral Ganglion of Helix pomatia. X40. C.T. Connective tissue. G.C. Large ganglion-cells. G.N. Ganglionic nuclei. T.L. Tentacular lobe. buccal ganglia and on the posterior surface of the cerebral, and small cells with a minimum of protoplasm, very similar to the ganglionic nuclei of Arthropods, crowded together upon the lateral surface of the tentacular lobes of the cerebral ganglia. The neuropile of the tentacular lobei derived from these cells is peculiarly dense. In the upper (isolated) specimen blue paper has been placed beneath the four nerves that rise from the visceral loop, and in the lower specimen the main features of the nerve distribution have been indicated by black ])aper. 0. C. 1305 A a. Nabias, Act. Soc. Linn. Bordeaux, ser. b, t. vii. p. 10. 54 PHYSIOLOGICAL SERIES. D. 51. A Slug {Limaw rufus), laid opcni longitudinally along tlic back, and with the viscera removed, to show the nervous system. The cerebral ganglia are pear-shaped and situated at some distance apart united by a commissure. They innervate the same organs as in the Snail. The oesophageal uervous ring is completed below the gut by a larger ganglionic mass from which nerves radiate to supply the body. The principal nerves are the two inferior ones which extend on either side of the mid-line of the ventral surface straight to the hinder end of the body, giving off branches from their outer sides to the muscular foot. A small asymmetrical ganglion is formed on the nerve that supplies the heart and respiratory apparatus. The suboesophageal ganglion is a compound body, formed, as in the Snail, by the fusion of the pedal, pleural, and visceral ganglia. 0. C. 1304. Hunterian. D. 52. The same species of Slug laid open along the ventral aspect, and with the viscera removed to show more especially the suboesophageal ganglion and its nerves. A bristle occupies the place of the oesophagus. 0. C. 1305. Hunterian. D. 53. A Slug (Lima.v sp.) with the body-walls divided longi- tudinally along the ventral surface, and divaricated to show the nervous system in position. Preserved in Goadby solution. D. 54. Two isolated specimens of the nervous system of a Pond- Snail {Limncea stagnalis). The central nervous system although decidedly concentrated is much less so than in the Land-Snail. The three pairs of ganglia that form the circum-oesophageal ring (cerebral, pleural, and pedal) are independent and joined together by short commissures and connectives. The orthoneurous visceral loop is extremely short, yet its ganglia and the fibrous strands that unite them to one another and to the pleural ganglia cim be clearly distinguished. Tiw. distribution of the nerves that arise from the various ganglia corresponds in the main with that seen in Ileli.v, but it should be noticed that at the end of one of the terminal branches of the pallial nerve given I NEEVOUS SYSTEM. — INVERTEBRATA. 55 oS from the right visceral ganglion there is a small round ganglion ; this underlies a sensory pit (probably olfactory) situated close to the respiratory orifice. The cerebral ganglia are considerably lobulated. Blue paper has been placed beneath the visceral loop in both specimens. 0. 0. 1305 A Lacaze-Duthiers, Arch. Zool. Exp., t. i. 1872, p. 437. L. 55. Two specimens of the nervous system of a Sea-Hare {Aplysia punctata), seen from the dorsal aspect, isolated (upper specimen), and in situ. The several ganglia of the circum- oesophageal ring are separate, definite in outline, and of moderate size. The cerebral ganglia lie close together above the oesophagus, on either side of which they are united by a pair of short connectives to the pedal and pleural ganglia. Each pleural ganglion lies shghtly behind and below the pedal ganglion of the same side, joined to it by a very short connective. The pedal ganglia are united by two commissures — one short and stout passing directly from ganglion to ganglion, the other longer and more delicate. The pleural ganglia give rise to a long untwisted (ortho- neurous) visceral loop, that extends backwai'ds through the cavity of the body to the pericardium. Here it is completed by a large bilobed ganglion, from which nerves are given off to the body-wall, generative organs, and gill. The branchial nerve arises from the upper of the two lobes, and at the base of the gill forms a small round ganglion that underlies a special sense-organ (osphradium) . The chief nerve given off from the lower lobe supplies the genital organs. Although the visceral loop is essentially ortho- neurous, it shows a variable but distinct tendency towards a streptoneurous twist. When seen from above its left arm appears in the posterior part of its course to lie directly beneath or even in some cases slightly to the right of the right arm. This partial streptoneury is interesting in view of the unmistakably twisted loop of another Opisthobranch {Action). The nerve distribution resembles that in other Gastropods ; the sense-organs of the head and the integu- ment around the mouth are supplied from the cerebral ganglia ; the pleural nerves innervate the anterior parts of 56 PHYSIOLOGICAL SERIES. the lateral body-walls, while the ventral and posterior parts of the body receive nerves from the pedal ganglia. The buccal ganglia are contiguous in the mid-line ; they lie on the posterior surface of the buccal mass between the oesophagus and radula-sac, and give oflf nerves as usual to the buccal mass and alimentary canal. D. 56. A Sea-Hare (Aphjsia sp.) opened longitudinally to the right of the dorsal mid-line, and with the body-walls spread to either side to show the nervous system i?i situ. The viscera have been removed with the exception of the buccal mass and part of the heart. The outlines of the ganglia are less distinct than in the previous specimen, as the connective-tissue sheath by which they are enveloped has not been removed. Preserved in Goadby solution, D, 57. Two specimens of the nervous system of a Nudibranch {ArcJiidoiis tuherculata) . The central system is extremely concentrated. It consists of a single supra-cesophageal lobulated mass, in which can be traced three pairs of centres that apparently represent cerebral, pleural, and pedal ganglia. The cerebral, which form the anterior part of the mass as seen in the lower specimen, give otF, as usual, buccal connec- tives and nerves to the cephalic sense-organs. The pleural and pedal centres supply the body-wall and generative organs. The lateral parts of the compound ganglion are u:nited below the oesophagus by a triple commissure ; two of its constituents arise in the pedal ganglia and correspond to the two pedal commissures of Tectibranchs (e.g. Aply.na), the third (marked by black paper in the upper specimen) unites the pleural centres and may be regarded as an orthoneurous visceral loop. 0. C. 1305 B a. D. 58. A Nudibranch (Tritonia homhergii) with the nervous system exposed from above. The central system consists of four ganglionic masses concentrated in a transverse band above the anterior end of the a3sophagus. The inner pair are contiguous with one another in the dorsal mid-line ; each rej)resents a fusion of a cerebral with a pleuro-visceral centre. From the anterior (cerebral) NERVOUS SYSTEM. — INVERTEBRATA. 57 l)ortion, nerves are given off to tlie integument and sense- organs of the head. The posterior (pi euro-visceral) part innervates the lateral and dorsal regions of the bodj^-wall. The two outer centres represent the pedal ganglia; they are in contact with the lateral surfaces of the pleuro-visceral centres ; each sends several large nerves to the foot. As in ArcUdoris the lateral parts of the supra-oesophageal mass are united below the gut by a triple commissure enclosed in a common neurilemma-sheath. Preserved in Goadby solution. V. Ihering, Anat. des Nervensystemes . . . der Mollusken, 1877, p. 174. CEPHALOPODA. Note.— In describing the Ceplialopod nervous system it has been assumed fur convenience' sake that the funnel and mantle-cavity are situated on the ventral aspect of the animal, and the beak at the anterior end. D. 59. The anterior parts of a male Pearly N"autilus {Nautilus pompilius) from which the viscera and left half of the body-walls and funnel have been removed to show the nervous system in situ,. The central system shows no differentiation into separate ganglia, but is coated evenly in all parts by a continuous layer of ganglion-cells ; it is situated entirely within the head region, supported by the upper part of the large cephalic cartilages. Above the oesophagus lies a transverse cylindrical bar of nervous tissue directly continuous at either end with an antero-posteriorly flattened optic ganglion. The extremities of the supra- u?sophageal bar are connected below the (jesophagus by two semicircular nervous bands that rise by a common origin from either end of the bar and slant respectively for- wards and backwards towards the ventral surface of the oesophagus. The anterior semicircular band is thick at either end, but rapidly tapers towards its middle, until beneath the oesophagus it forms a narrow com- missural strand. It gives off on either side from the lower end of its thickened region a stout nerve for the funnel, and from its anterior surface, between this point and its junction with the supra-resophageal bar, a large number of nerves for the outer and lateral series of tentacles. PHYSIOLOGICAL SERIES, One of those on the left side is larger than the rest and innervates the spadix — an accessory sexual organ in the male formed by the modification of certain of the tentacles of the lateral series. The posterior semicircular band is of equal calibre throughout. From the hinder margin of its lateral parts a series of nerves are given off to the body- muscles, as well as a pair on either side to the posterior region of the funnel. From its postero-ventral border it gives rise to two large nerves that run backwards upon the ventral surface of the body to the neighbourhood of the gills ; here each gives off two branchial branches and is said to then continue onwards to terminate among the viscera (this continuation is not shown). "Nerves from the supra- CESophageal bar supply the olfactory tentacles and pit, the otocyst, and parts of the hood. This centre also gives origin near either end to two strong connectives, that after a sinuous course join a ganglion (pharyngeal ganglion) upon the lateral surface of the buccal mass. The pharyngeal ganglia of opposite sides are united beneath the gut by two commissures, one of which passes anteriorly along the inner border of the lower beak, giving off two large nerves to the tissues within it, while the other passes transversely between the oesophagus and radula-sac and has upon its course a pair of buccal ganglia from which nerves are distributed to the buccal mass and oesophagus. Although the central nervous system shows a certain degree of specialisation in being concentrated in the head, it is on the whole in a very simple and primitive condition, and reminds one, especially in the band-like form of its several parts and the diffuse distribution of ganglion-cells upon its surface, of the condition observed in the Amphi- neura. The three nervous bands of which it is composed probably represent the typical centres of the Mollusca in a state of great simplification, namely : — cerebral (supra- oesophageal bar) for the innervation of the head region with its sense-organs, pedal (anterior semicircular band) innervating the tentacle complex and the funnel, and pleuro-visceral (posterior semicircular band) for the mantle, gills, and viscera. 0- C 1306 A a. Graham Kerr, Proc. Zool. Soc. 1895, p. G73. NERVOUS SYSTEM. — INVERTBBRATA. 59 D. 60. The anterior or muscular part of the body of a female Pearly Nautilus {Nautilus pornpilius) laid ojDen longitudin- ally along the dorsal aspect, and with the sides divaricated to show the nervous system. In the female the inner ring of tentacles consists not only of two lateral groups, as in the male, but also of a ventral series located in two lobes that lie one on either side of the ventral mid-line. A pair of large nerves (the left one is indicated by black paper) for the innervation of these are given off from the anterior suboesophageal baud on the outer side of the funnel- nerves. Each enlarges as it nears the tentacular lobe to form a triangular ganglion, from which branches radiate to the individual tentacles. 0. C. 1306 A. Owen, Memoir on the Pearly Nautilus {Nautilus ■pornpilius), 1832, p. 36. D. 61. The head of a Cuttle-fish [Sepia officinalis) dissected from the dorsal aspect to show the form and position of the central nervous system. It is extremely concentrated, and forms a compact ring around the fore part of the oesophagus protected externally by a cartilaginous capsule. The ring is divisible into a pyriform supra-oesophageal mass (cerebral ganglion) and a larger oblong suboesophageal ganglion, united together on either side of the esophagus by stout connectives. The cerebral ganglion is joined on either side by a short stalk to a large kidney-shaped optic ganglion, from whose distal margin a number of nerve-fibres arise and perforate the cartilaginous optic capsule to reach the retina. Upon the dorsal surface of each optic stalk there is a small rounded excrescence from which the olfactory nerve takes its origin (see Olfact. Organs, Section E). Upon the right side bristles have been placed beneath the superior ophthalmic nerve— a small nerve that rises from the hinder part of the suboesophageal mass close to the base of the circum- oesophageal connective, and innervates the globe of the eye and the integument on its dorsal surface. 0. C. 1306 D. 60 PHYSIOLOGICAL SERIES. D. 62. Tlio central nervons system of a Cuttle-fish {Sepia officin- alis), isolated to show the relations of its parts, the origin of the main nerves, and the anterior portion of the visceral system. The pointed anterior extremity of the cerebral ganglion is joined by a pair of connectives to a small independent ganglion (snpra- pharyngeal), which is probably a dis- connected piece of the cerebral ganglion and not a part of the visceral system. This ganglion is situated on the dorsal surface of the oesophagus close behind the buccal mass, and innervates the peristomial membrane by a number of nerves that radiate from its anterior margin. It is united to the anterior part of the suboesophageal mass by a pair of connectives, that rise from its posterior surface, and by a second pair from its outer extremities to a buccal ganglion that lies below the oesophagus on the posterior wall of the buccal mass. Nerves from this latter centre supply the buccal mass, radula, and alimentary canal. The cerebral ganglion is further united by connectives to the suboesophageal mass. There are two on either side— a small one that arises from its anterior extremity and joins the suprapharyngeo-suboesophageal connective close to the suboesophageal mass, and another, extremely short and stout, that forms the lateral part of the circum-oesophageal ring below the optic stalk. This last is superficially single, but internally two fibrous strands can be distinguished that pass respectively to the anterior and posterior parts of the suboesophageal mass, and represent cerebro-pedal and c-,erebro-pleural connectives. The suboesophageal mass may be divided into an anterior and a posterior region. The anterior innervates the arms and fore part of the funnel, and may be regarded as a pedal ganglion. The posterior region contains the paUial and visceral centres; it projects backwards beyond the cerebral ganghon and gives off three large pairs of nerves respectively to the mantle, to the posterior part of the funnel, and to the viscera and gills: two smaller pairs arise from its dorsal and ventral surfaces and innervate the superficial parts of the eyes 0. C liiUb F. Pelseneer, Arch. Biol., t. viii. p. 723. NERVOtJS SYSTEM. — INVERTEBRATA. 61 D. 63. The isolated nervous system o£ a Cuttle-fish {Sepia officin- alis) showing the origin and conrse of the main nerves. The innervation area of the cerebral ganglion includes the eyes (through the mediation of the optic ganglia), the olfactory pit, the otocyst (by nerves that perforate \he suboesophageal mass), and, indirectly through the supra- pharyngeal ganglion, the lips. The anterior (pedal) region of the suboesophageal mass is composed of a brachial and an infundibular centre. The brachial nerves arise from the anterior margin of the former ; they are 10 in number — 8 for the non-retractile arras and 2 for the tentacles. Just before the separation of the 8 arms from their common muscular base, their nerves are united together by a circular commissure, the main part of which enters a small ganglionic enlargement upon each brachial nerve, while a smaller strand leaves the connnissure on one side of the ganglion, passes across its inner surface, and joins the commissure again on the other side. In the free part of each arm the nerve is central in position and ganglionic. The nerves for the anterior part of the funnel arise from the ventral surface of the in- fundibular centre — their extremities can be seen in the specimen projecting beyond the optic ganglia. A pair of large mantle-nerves are given off from the lateral posterior corners of the pleuro-visceral centre. Each of them runs diagonally backwards to the retractor capitis muscle ; at this point it gives off" a branch from its inner margin, and then passes through the substance of the muscle to the dorsal wall of the mantle- cavity. Here it divides into two branches, one of which shortly enters a large round ganglion (g. stellatum), from which nerves radiate to all parts of the mantle; the other passes along the median surface of the stellate ganglion and is distri- buted to the lateral-fin fold. The posterior infundibular nerves arise slightly in front of the pallial, from the ventral surface of the pleuro-visceral centre. The visceral nerves are given off close side by side from its posterior border. They run backwards to the ventral surface of the gastric gland, perforate the subhepatic cartilage and continue close beneath the skin, one on either side of the cephalic vein to 62 PHYSIOLOGICAL SERIES. the external renal openings. J ust posterior to the subhepatic cartilage, each nerv(! gives off a branch from its lateral surface to the retractor infundibuli, and a little further back a second branch from its median side to the rectum and ink-sac. Dorsal to the external renal openings the two main trunks are united by a plexiform commissure, and from this point continue along the antero-lateral margin of the kidneys till they reach the bases of the gills. Here each forms a ganglion and passes forwards along the gill to its anterior end. Numerous delicate fibres from the plexiform commissure ramify amongst the viscera and establish con- nections with a large splanchnic ganglion situated upon the stomach. The splanchnic ganglion is further connected to the buccal ganglia by an extremely fine pair of nerves that lie upon the walls of the oesophagus. From the active predaceous habits of the Dibranch Cephalopods and the great concentration of their central nervous system, one may conclude that the latter is a highly- specialised and efficient organ, but as to its actual working little definite is known. It may be said, however, that : — The cerebral ganglion (in certain cases at any rate, though apparently not in all) exerts a general inhibitory influence over the rest of the system. In its anterior part is located a centre for the fixation of the arm-suckers, their relaxation depending on another centre in its posterior part. Each brachial nerve forms' it reflex centre for the general movements of the arm in which it lies. The pleuro-visceral mass, and not as miglit be supposed the stellate ganglion, is the reflex centre for the respiratory movements of the mantle ; it is also the controlling centre for the chromatophores. The action of the heart can take place independently of the cephalic central system, although its pulsations are regulated by the suboesophageal mass. 0. C. 1306 E. Chf5ron, Ann. Sci. Nat., ser. 5, t. v. 1866, p. 41. D. 64. A section of the mantle of a large Cuttle-fish (Sepia oficinalis) showing one of the pallial nerves with the ganglion stellatum. The branch of the pallial nerve that NBKVOUS SYSTEM. — PROTOOHORDATA. 63 passes without being implicated in the ganglion, through the substance of the mantle to the muscle-fibres of the lateral fin, is indicated by a black bristle. 0. C. 1307. Hunterian. PROTOCHORDATA. TUNICATA. D. 65. A Simple Ascidian (Phallusia mammillata) from which the dorsal parts of the test have been removed to show the nervous system. In the adult this is in a much reduced condition ; it is minute compared with the bulk of the animal, and consists of a rod-like ganglion that lies on the muscular body- wall upon the dorsal surface between the oral and atrial apertures, close in front of the latter. From either end it gives off" a pair of nerves that respectively innervate the integument and muscles of the oral and atrial siphons. A few small nerves for the general body-wall arise from its lateral parts. The hinder end of the ganglion is prolonged backwards as a fine ganglionic cord, that runs along the dorsal edge of the branchial sac and terminates upon the liver. This cord (visceral cord) apparently inner- vates the anterior region of the alimentary canal ; it has been shown to be the degenerate remains of the portion of the larval dorsal cord that lies between the cerebral vesicle and the tail. 0. C. 1307 A. Presented by Prof. C. Steioart. Van Beneden & Julin, Arch, de Biol., t. v. 1884, pp. 317 & 633. CEPHALOCHOEDA. D. 66. The isolated central nervous system of a Lancelet {Amphioxus lanceolatus) showing its general form and some few of the spinal nerve roots. The central nervous system in Amphioxus consists of an unsegmented tubular cord of roughly triangular cross section. At either end it narrows to a point, but otherwise is of approximately similar calibre throughout. It lies upon the dorsal surface of the notochord, extending from its hinder extremity to a point some little distance behind its anterior end. The 64 PHYSIOLOGICAL SERIES. anterior pointed region terminates in a mt^dian eye-spot and gives off two pairs of purely sensory nerves to the snout. From the rest of the cord a series of mixed and motor nerves arise, that correspond in number and jiosition to the septa -between the myotomes and consequently alternate on eitlier side. The central canal is lined by a sup- porting epithelium. This is surrounded, as in Vertel)rates, by a layer of ganglion-cells, while the outer parts of the cord consist of non-medullated nerve-fibres of different sizes. Some uf these, which arise from giant pantdion-cells that lie across the canal in the anterior and posterior thirds of the cord, are of remarkably large size and remind one of Miiller's fibres in Cyclostomes or of the giant fibres in Invertebrates. In front the canal broadens out to form a cerebral vesicle, that probably corresponds with the three primary vesicles of the vertebrate brain. A small evagina- tion of its dorso-anterior wall extends towards the olfactory pit and indicates the last closed connection of the central canal with the exterior (a similar excrescence occurs in the embryos of Vertebrates) ; while below, another median evagination apparently represents the infundibulum. As the walls of this " brain " region are thinner than in other parts of the cord, there is no external sign of a cerebral enlargement, 0. C. A. 1347. Willey, ' Amphioxus/ 1894, p. 82. VERTEBRATA. BRAIN. Edinger, Anat. (central Nervous System, 5th ed. (Engl, trans.) 1899. Edinger, Abhandl. Senckenberg. Gesell., Bd. xv. 1890 {Cerebritm) . Haller, Morph. Jahrb., Bd. xxvi. 1898, p. 632 {Biblioa.). PISCES. CYCLOSTOMI. D. 67. The brain of a Sea Lamprey [Petromyzon marinus). The Cyclostomes have an extremely simple brain, NERVOUS SYSTEM. — VBRTEBRATA. 65 similar in many respects to that of a low Urodele or to the embryonic stages of higher Vertebrates. It consists o£ a slight enlargement of the anterior end of the cord accompanied by a corresponding increase in the size of the central canal and its partial transverse division into three ventricles. Upon this foundation certain excrescences have been developed in connection with the senses of sight and smell. The dorsal wall is to a very large extent purely epithelial, nervous matter being mainly confined to the floor and side walls. The primitive condition of the brain is also shown by the relatively large size o£ the ventricles, Fig. 19. Brain of Petromyzon marinus (enlarged). [For list of abbreviations, see page 508.] and by the absence o£ any special thickenings of their nervous walls. The medulla forms nearly half the brain (fig. 19, A). It passes behind insensibly into the cord, and in front is laterally expanded with separation of its walls in the mid-dorsal line to enclose a large pyriform opening (fossa rhomboidalis) covered by a thin vascular membrane. This roof consists of an epithelium continuous with that lining the fourth ventricle, of pia mater and blood-vessels ; it is considerably larger than the fossa and in consequence projects in all directions into the cranial cavity, and in VOL. u. F PHTSIOLO(}ICAL I3RRIES. conjunction with the similar vascular roof of the optic lobes spreads out over a large part of the dorsal surface of the brain. These two choroid plexuses have been removed together and mounted at the side with their under surfaces exposed to show the complicated folding of their walls (fig. 19, B). The roof of the medulla behind the open rhomboid fossa is slightly thickened on either side of the mid-line, and here gives origin to the hinder roots of the vagus (the roots are not shown in the specimen) . Similar thickenings in the lateral walls of the fossa give origin to the 7th and 8th cranial nerves, and another pair of swellings in the floor of the fourth ventricle, seen through the open rhomboid fossa, are the motor nuclei of the 5th pair of nerves. The floor of the fourth ventricle is indented in the mid-line by a sharp furrow, on either side of which is a slight thickening due to a pair of tracts (fasciculi longitudinales posteriores) that connect the thalamencephalon with the cord and on their way form connections with the motor nuclei of the cranial nerves. They are particularly well marked in Fishes. The rhomboid fossa is bounded in front by a narrow but slightly thickened lip — the cerebellum. The mid-brain con- sists above of a pair of very prominent rounded eminences — the optic lobes. They contain a common ventricle derived from the aqueduct of Sylvius and are superficially separated from one another in the dorsal mid-line by a groove. Their walls are composed for the most pai*t of nervous tissue from the outer surface of which the optic nerves are given off, but this is replaced at the anterior end by an epithelial choroid plexus (the fore part of the speci- men at the side) similar to that covering the rhomboid fossa. The removal of this plexus has exposed a minute opening situated at the anterior end of the optio lobes and bounded in front by a band of commissural fibi*es (posterior com- missure)— not externally visible — that marks the bouudar}' line between the mid-brain and thalamencephalon or primary fore-brain. The thalamencephalon is remarkably deep from above downwards. Its roof is epithelial in its anterior part and NERVOUS SYSTEM. — VBRTEBEATA. 67 projects beak-like above the cerebrum, but posteriorly it is nervous and swollen to form an asymmetrical pair of ganglia (ganglia liabenulse), the smaller (left) of vfhicli is in con- nection with the pineal body. In the specimen these ganglia can only be distinguished as a single median thickening in front of the optic lobes. The ganglia habenulas are one of the most constant parts of the vertebrate brain. They are always present on either side close in front of the epiphysial evagination, are united by a commissure, and are always in connection by tracts with the olfactory area of the cerebrum and with the corpus interpedunculare. The latter can be seen in the specimen as a small median protuberance close behind the origin of the oculo-motor nerves. The floor of the thalamencephalon is expanded ventrally to form a capacious infundibulum. Lobi inferiores and saccus vasculosus are absent, but there is said to be a well marked saccus infundibuli in the posterior wall of the infundibulum. A similar structure occurs in Elasmo- branchs and embryo Teleosts. The side walls consist mainly of tracts that connect the cerebrum with the more posterior regions of the brain. They are covered super- ficially by the optic tracts on their way downwards and forwards from the optic lobes to the chiasma in front of the infundibulum. The thalamencephalon is continuous at its anterior end, on either side of the mid-line, with a pair of hollow lobes — the secondary fore-brain — each consisting of two parts : a posterior lobe (the hemisphere), and a larger anterior lobe (the olfactory bulbj from which a nerve is given off to the nose. A sHght lobulation observable upon the surface of the olfactory bulbs is due to a glomerular condensation of the neuropile close beneath the surface. The hemispheres are mesially united by a commissure (anterior commissure) that lies in the dorsal parts of the anterior wall of the thalamencephalon (lamina terminalisj. They have ganglion-cells scattered irregularly throughout their walls and show no signs of cortical structure. Ahlborn, Zeits. wiss. Zool., Bd. xxxix. 1883, p. 191. 68 PHYSIOLOGICAL SEniES. ELASMOBEANOHII. Miklucho-Maclay, Beitiiige z. vergl. Neurol. 1870. Edinger, Arch. mikr. Anat., Bd. Iviii. 1901, p. 661 {Cere- helluvi) . The brain of the Elasmobranchs only partially fills the cranial cavity. It has generally an elongated narrow form, with the several regions lineally arranged and, except in the case of the cerebellum, with but little overlapping of parts. It is chiefly remarkable for the great development of the centres in connection with the sense of smell— olfactory bulbs and peduncles, and cerebrum. The lamina terminalis is more or less thickened— excessively so in Kays— and frequently is indented m the mid- line to form small lateral ventricles. The optic lobes are well marked, as are also the several parts of the hypo- thalamus (infundibulum, lobi inferiores, saccus vasculosus and saccus infundibuli) . The cerebellum, as in Bony Fish and Birds, is strongly developed; it overlaps the optic lobes and medulla to varying degrees and frequently shows complex transverse folding. Posteriorly it is continued into the convoluted margins of the rhomboid fossa (medullary auricles). In Sharks the medulla is usually long and without definite separation from the cord, but is much shortened in Rays. It owes its large size mainly to the great development of the nuclei of the cranial nerves, especially those in connection with the respiratory nerves (x.) and the sensory nerves of the skin (v. and the lateral- line nerves). It also contains great longitudinal motor tracts (fasciculi longi- tudinales posteriores) in its floor, besides less developed tractsin connection with the optic lobes (fillet) and cerebellum. The walls of the brain are nervous except for the vascular epithelial roof of the rhomboid fossa and third ventricle. There is no sign of cortical formation in the cerebrum, but its walls consist of^a relatively thin outer molecular stratum and a thick cellular layer surrounding the ventricles. In its base definite cell-masses give rise to the anterior commissure and to longitudinal tracts that pass to a large ganglion (nucleus rotundus) in the thalamus, which in turn gives off fibres to the hinder parts of the brain. A second pair of tracts pass from the cerebi-al roof (pallium) into the base of the thalamencephalon, and decussate behind the optic chiasma in close contiguity with tracts from the base of the NERVOUS SYSTEM. — VERTEBRATA. 69 mid-brain (deciissatio post-optica). The thalamencephalon also contains in its dorsal parts a pair of ganglia habenula3 connected by tracts with the olfactory parts of the cerebrum, and with the tectum opticum, corpus interpedunculare (Meynert^s i bundle), and hypothalamus. In the lower parts of the thalamus lie another pair of gangHa (g. geniculata) situated under cover of the optic tracts. They are very constant throughout vertebrates and contribute fibres to the opticus. The hypothalamus, whose walls consist of a fibrous reticulum interspersed with numerous ganglion-cells, is the chief point of origin of the great fasciculi longitudinales posteriores ; it is also connected with the cere- bellum and tectum opticum. In the roof of the mid-brain (tectum opticum) there are two chief layers— an outer layer consisting of the roots of the opticus and containing numerous ganglion-cells in its deeper parts ; and a deep fibrous layer in which the fibres for the most part run transversely and constitute a tectal commissure, thickened in its anterior parts to form the posterior commissure. On either side the fibres pass backwards into the medulla (some crossing in the floor as the commissura ansulata), and constitute the anterior termination of a large sensory tract (fillet) that extends into the cord and is connected in the medulla with the sensory cranial- nerve nuclei. Part of this tract arises from a nucleus in the posterior part of the tectum— the homologue of the posterior corpora quadrigemina of Mammalia. A nucleus of large cells (roof nucleus) lies in the mid-line at the hinder extremity of the tectum beneath the transverse commissure ; its meaning is doubtful, though probably it is a nucleus of the trigeminal nerve. The cerebellum consists, as in all vertebrates, of four layers- molecular, intermediate (Purkinje's cells), fibrous, and nuclear ; the fibrous being situated external to the nuclear, and not as in Teleosts, Birds, and Mammals, on its deep surface. The layers vary in thickness in different regions, the nuclear for instance being almost entirely concentrated in a pair of ridges, one on either side of the mid-line (longitudinal zones). Tracts connect the cerebellum with the thalamencephalon, mesencephalon, and spinal cord, but the greater part of the fibrous layer is in direct connection with the sensory cranial nerves. 70 PHYSIOLOGICAL SERIES. SQUALIDA. 38, The brain of Notidanus griseus exposed within the skull from the dorsal and ventral aspects. The Elasniobranch brain is found in its simplest and most primitive condition in the NotidanidaB, and presents in them many features that in other members of the class are transient, occurring only during certain developmental stages. The following characters should be particularly noticed as indications of primitive construction : — The rela- tively great length and narrowness of the brain ; the absence of any marked local thickening of its walls ; their general thinness and the consequent spaciousness of the ventricles (for these and other internal features see Maclay, t. ii, fig- 12) ; the simple unconvoluted cerebellum ; the great development of the medulla, its length, wide dorsal open- ing, and gradual passage into the cord. The fore-brain (cerebrum) is deeply cleft anteriorly (more so than in any other Elasmobranch) by an infolding o£ the lamina terminahs ; its cavity is thus separable into a posterior unpaired chamber — the fore part of the third ventricle — passing in front into a pair of anteriorly directed pockets, or lateral ventricles. The latter are continuous at their anterior end with the cavities of the long olfactory peduncles, by means of which the olfactory bulbs, which are situated directly beneath the olfactory organ, are connected to the rest of the brain. The olfactory bulb has always in Elasmobranchs (except it seems in Echinorhinus) this close relation to the olfactory organ, so that the length of the peduncle varies in different forms according to the position of the organ with regard to the brain. The peduncle is usually, as in this case, hollow, but sometimes when very long it is solid ; it has the same structure as the olfactory bulb, and together with it is an outgrowth from the fore-brain. The thalamencephalon is comparatively short and wide. The fore part of its roof is membranous and forms a conical sac-like protrusion (paraphysis) between the hemispheres. The hinder part is concealed by the optic lobes ; it contiiins the gaugUa habenulaj and gives origin to the thread-like NERVOUS SYSTEM. — VBRTEBRATA. 71 epiphysis. The floor is evaginated in the mid-line to form the infundibulum. This is hidden in the specimen by the hypophysis — an ectodermic glandular structure closely attached to its ventral surface. The lateral parts of a large vascular dilatation of the posterior wall of the infundibulum (saccus vasculosus) can be seen protruding beyond the lateral parts of the hypophysis. On either side of the infundibulum, in front of the saccus vasculosus, are a pair of globular enlargements — the lobi inferiores. Each of them contains a cavity (not shown) in connection with that of the infundibulum. The optic lobes are of considerable size, although neither here nor in any other member of the group do they reach th e size and importance that they do in most Teleostean fishes. They are oval in form, separated dorsally by a superficial longitudinal groove, and contain a large com- mon cavity. Their posterior part is covered by the anterior lobe of the cerebellum. No part of the Elasmobranch brain is subject to more variation than the cerebellum ; in this species it occurs in its simplest form, although well developed when compared with that of certain other Vertebrate groups (e. g. Cyclostomes, Amphibia). It is superficially perfectly smooth except for a shght median longitudinal furrow, and when seen from above is diamond- shaped with pointed anterior and posterior lobes, within each of which extends a part of the common cavity. A single median opening leads from the latter into the fourth ventricle. On either side of the posterior cerebellar lobe lies a convoluted portion of the thickened margin of the rhomboid fossa ; this ridge (medullary auricle) is clearly seen on the left side ; it passes to the mid-line under cover of the posterior lobe of the cerebellum ; here meets with its follow of the opposite side, without fusion, and then, turning abruptly upwards into the cavity of the cerebellum, forms a projecting longitudinal ridge (dorsal longitudinal zone of Burckhardt) that runs close beside the mid-Hne to its anterior extremity. From their microscopic structure the medullary auricles should bo included in the cerebellum. The course of this pair of zones is not visible in the specimen after they pass under cover of the cerebellum. 72 PHYSIOLOGICAL SERIES. The medulla is large and remarkably long, with an exten- sive rhomboid fossa roofed over by a thin pleated vascular membrane (turned to one side in the specimen). Within the cavity certain ridges and swellings— due to tracts and nerve nuclei— show with great clearness. A parti- cularly prominent pair on either side of the mid-ventral line are the fiisciculi longitudinales posteriores. On the outer side of these lie a pair of lesser swellings— the meter nuclei of the vagus ; and outside these again, on the lateral walls of the ventricle, another very pronounced pair, re- markable for their beaded appearance. They are the sensory nuclei of the vagus. In front they pass under cover of the auricles. In the swollen border of the rhom- boid fossa, just before it bends to form the auricles, lie the nuclei of the acusticus and lateral hne (tuberculum acusticum and lobus lineae laterahs). 0. C. 1311 Bd. Presented hy Dr. Albert Giinther. D. 69. The brain of a Greenland Shark {Lcemargus borealis). This brain differs little in its essential features from that of Notidanus. In detail the following differences are ap- parent : — The lamina terminalis is not so deeply indented, so that although the fore-brain is clearly separable into unpaired posterior and paired anterior regions, the latter are not so prominent. The optic lobes with their associated tracts and nerves are far less developed. The cerebellum is relatively larger and extends forward to the anterior border of the optic lobes. It shows upon its dorsal surface a shallow transverse indentation — the first indication of the transverse folding so strongly marked in some of the higher Elasmobranchs. The dorsal walls of the cerebrum and thalamencephalon have been turned to one side, exposing the cavities of these parts and showing in the floor of the third ventricle a long slit leading into the infundibulum, saccus vasculosus, and lobi inferiores. The latter are prominent and about equal in size to the optic lobes. The thalamencephalon roof is epithelial and vascular ; it is much convoluted on its inner surface, and forms a choroid plexus that hangs within the NERVOUS SYSTEM. — VERTEBRATA. 73 third ventricle and extends slightly into the lateral ven- tricles. The cerebellum has been divided in the mid-line, and the two halves have been separated to show the large cerebellar cavity and the course of the longitudinal zones along the roof on either side o£ the mid-Kne. The latter are specially well seen coursing backwards upon the ventral wall of the anterior lobe. The floor of the fourth ventricle has been exposed by turning the vascular roof to one side. Owing to the divi- sion of the cerebellum and to the somewhat unnatural separation of the side walls of the medulla, the fore parts of the fasciculi longitudinales and of the vagal lobes are brought into view. The fine transverse strands visible at intervals on either side of the fasciculi posteriores are tracts connecting them with the motor nuclei of the cranial nerves. The motor nucleus of the vagus and the relation of the root of the superficial ophthalmic lateral-fine nerve to the lobus finese laterafis are particularly clear. O.G. 131 Lb c. Presented hy W. Coivan, Esq. D. 70. Parts of the cranium of a Spinous Shark {Ecliinorhinus spinosus) with the brain shown from the dorsal aspect. This brain, like those of the two other representatives of the Spinacidse (Acanthias and Lcemargus), is of an essen- tially simple type. This is particularly shown by the relatively large size of the meduUa (it occupies about half the brain-length), its extensive rhomboid fossa and gradual passage into the cord. The cerebellum is rounded and, for that of an Elasmobranch, very poorly developed ; it shows a feeble transverse groove. The parts of the brain in front of the cerebellum are somewhat indefinite in outline owine to imperfect preservation, but it can be seen that the optic lobes and nerves are small, the thalamencephalon fairly long, and the cerebrum of medium size, without median division and apparently with a considerable cavity. From either side of the cerebrum is given off" an immense solid olfactory nerve, without however any cor- 74 PHYSIOLOGICAL SERIES. responding development either of the fore-brain or of an olfactory bulb; in fact it is stated that an olfactory bulb is absent. This marked disproportion in development between the olfactory nerves and the cerebrum, with the apparent absence of definite olfactory bulbs, suggests that the nerves, although evidently to a great extent fibrous, probably also have the nature of olfactory centres ; it should be noticed in this connection that shortly before entering the cerebrum, each olfactory nerve undergoes a very perceptible enlarge- ment. The poor development of the optic parts of the brain are probably to be accounted for by the deep habitat of this Shark. The brain occupies only a small part of the spacious cranial cavity. This preparation is from a fish caught off the coast of Cornwall. O.C. 131lBa. Presented hy F. Buckland, Esq. Jackson & Clarke, Journ. Anat. & Physiol., vol. x. 1876, p. 76. D. 71. Part of the skull of a Spiny Dog-fish (Acanthias vulgaris) with the brain exposed from the dorsal and ventral aspects. This is a simple brain like the preceding specimen, but shows certain differences that foreshadow more pronounced features in the relatively complex brains of higher Sharks; such are a pair of indistinct rounded eminences upon the dorsal surface of the fore-brain at its hinder end, and the deepening of the transverse cerebellar furrow. The median indentation of the fore part of the cerebrum is strongly marked and terminates on the dorsal surface in a rounded pit — a nutritive foramen of very constant occurrence among Elasmobranchs. The olfactory peduncles are slender and of moderate length with small oHactory bulbs ; on the other band, the visual organs and optic lobes are very strongly developed. The lobi inferiores are also well marked and oval in form. The medulla does not differ in any important way from that of previously described primitive forms. Its cavity is exposed on the right side. D. 72. Part of the cranium of a Spotted Dog-fish {Sci/llium calulus) with the brain in situ. This brain, in comparison NBBVOUS SYSTEM. — VBRTEBRATA. 75 with those previously described, shows a noticeable increase in the size of the parts in connection with the olfactory organs (olfactory bulbs, peduncles, and cerebrum) . On the other hand, the optic region is weak. The olfactory bulbs are each partially divided into a right and left half by a shallow groove— an indication of incipient duplicity, of interest in view of the complete separation of the olfactory bulbs into two parts in Careharias. They are united by short thick peduncles to the lateral parts of the cerebrum. The latter is strongly convex in front and shows but slight indications externally of separation into lateral lobes :*'its postero-dorsal parts are raised to form a pair of rounded eminences similar to those seen in AcantMas. The cerebrum is continuous behind with the remarkably long and narrow thalamencephalon. The tela choroidea forms a close-fitting membranous roof to this region, and shows very clearly between its posterior fourths an opaque band— the com- missura habenulte. The epiphysis, which rises close behind this commissure, is long and thread-like as in most Elasmo- branchs; it extends forwards over the cerebrum and terminates on a level with the olfactory bulbs in a thickened end. In this and most other genera it is said to be solid except close to the brain, and to consist of cells embedded iu a finely granular intercellular substance. The cerebellum is quite simple, though of some size ; it has a median longitudinal furrow and slight lateral ind'en- tations. (The asymmetry noticeable in this cerebellum is probably unnatural, due to distortion during hardening.) The medulla is of a higher type than in the previous speci- mens ; it is shorter and broader and has a more definite hmit towards the cord. The brain fills the greater part of the cranial cavity, D. 73. The brain of a Spotted Dog-fish {Scijllium catulus) opened to show its internal structure (fig.20) . The roof of the cere- brum has been removed to show the direct continuity of the unpaired part of the cerebral cavity with the third ventricle behind, and with the lateral ventricles in front. The latter are separated by a thick median septum, and are continued from their posterolateral parts through the olfactory 76 PHYSIOLOGICAL SERIES. peduncles to the ventricles of the olfactory bulbs. The walls of the cerebrum are thick throughout, with no local swellings suogestive of corpora striata. On either side a choroid plexus projects downwards and forwards from the roof of the thalamencephalou into each lateral ventricle. Behind the cerebrum the brain has been longitudinally bisected and the two halves have been turned to either side. The saccus vasculosus has been opened from behind showing its cavity Fig. 20. LAT.VENT. OLF BULB. TEL.CHOR ,FOR. LOB. INF. ...GANG. HAB. POST COMM. LOB. OPT. CER. MED. AUR. Brain of Scyllium catulus (dissected). continuous with that of the infundibulum, as well as a ])air of large oval apertures in the lateral walls of the infundibulum that communicate with the ventricles of the lobi inferiores. In the floor of the thalamencephalou in front of the chiasma there is a small median pit (recessus praeopticiis), and at the point of union between the wall of the saccus vasculosus and the floor of the mid-brain, another (saccus infundibuH) which is found also in Cyclo&tomes and embryo Teleosts. NERVOUS SYSTEM. — VERTEBRATA. 77 Close behind the point of origin of the epiphysis, the cut edge of the roof o£ the brain is thickened by the presence of the posterior commissure. The mid- brain contains a considerable cavity (aqueduct of Sylvius) which sends lateral offshoots into the optic lobes. The roof (tectum opticum) of this region is moderately thick ; its division into outer and inner layers is very evident upon the section surface. In dividing the cerebellum the roof has been cut along its right lateral margin and turned aside entire with the left half of the" brain. The thin simple character of its walls^ and the complete course of the longitudinal zones from the medullary auricles to the boundary line between the cerebellum and mesencephalon are shown. D, 74. Part of the skull of a Basking Shark [Selache maxima) with the brain exposed from above. The brain is relatively small and somewhat shorter and broader than those pre- viously described ; it occupies a small part only of the spacious cranial cavity. The cerebrum is globular with thickened (?) walls, and is superficially without signs of lateral division. The olfactory bulbs and peduncles have been destroyed, but the rootof the (apparently solid) right peduncle can be seen rising from a slight eminence at the antero-lateral corner of the cerebrum. The thalamencephalon is very short, and is completely hidden in dorsal view between the cerebrum and optic lobes. The latter are of considerable size and are covered by the anterior lobe of the cerebellum. The cerebellum is large, with a series of twelve or so deep transverse fissures. The fish from which this dissection was made was caught in the North Sea ; it measured 12 feet in length. 0. 0. 1311 A b. Presented hy Dr. Albert Giinther. D. 76. A similar dissection of the hinder part of the skull of a somewhat larger Basking Shark {Selache maxima). The parts of the brain anterior to the optic lobes are absent. In this specimen the large size and convoluted structure of the cerebellum are very clearly shown ; it should be noticed that the median transverse furrow is more pronounced than 78 PHYSIOLOGICAL SERIES. the rest; it is the representative of the single furrow in such forms as Acanthias. The medulla is a good example of the elongated open type ; in it, the several prominences are very clear, more particularly the arrangement of the convoluted auricles and the lobus lineje lateralis. 0. 0. 1311 A. Presented hy Sir E. Home, Bart. 76. The brain of a Porbeagle {Lamna comuhica) divided in the median sagittal plane, and with the halves so mounted as to show the lateral and median surfaces. This brain (fig. 21) reaches a comparatively high state of development ; it is distinguished by its antero-j)osterior con- centration, the large size of the fore-brain and optic lobes, and the excessive development and structural complication of the cerebellum. The fore-brain is globular and, owing to the Fig. 21. OLF. BULB Bi-ain of Lamna rormihica, in sagittal section. immense thickening of the lamina terminalis, almost solid, its ventricle (best seen at the back of the left-hand specimen) being all but obliterated. The olfactory peduncles are narrow at their origin from the antero-lateral parts of the cerebrum and gradually become inflated as they approach the smnll olfactory bulbs. In this part their walls are extremely thin (see the cut edges of a square window in the figure). It seems likely that the small size of the olfactory bulbs is compensated by the great development of the cerebrum. The thalamencephalon is very short — compressed between the cerebrum and the large optic lobes. The latter are com- pletely covered dorsally by the cerebellum. The structure of the cerebellum is well shown in the right-hand specimen : NERVOUS SYSTEM. — VERTBBRATA. 79 although to all appearance nearly solid it will be seen to be formed of a single sheet of nervous tissue thrown into a complex series of transverse folds, between each of which penetrates a part of the general cavity of the organ. This complex folding is manifestly only a further extension of the simple transverse grooves seen in Acanthias or Galeus. The position of the original median transverse furrow is marked by the deepest and most complex fold. The lobi inferiores are small and open widely into the infundibulum. The medulla is considerably shortened antero-posteriorlv. 0. C. 1311 B 5. D. 77. The cranium of a Tope {Galeus communis) showing the brain in situ. The brain affords in its general construction and proportions an excellent example of that of an Elasmo- branch, in which all the typical features are strongly marked without any excessive specialisation of any one part. Thus it is long and narrow, though not so much so as in low types like Notidanus ; the optic and more especially the olfactory centres are highly developed ; the cerebellum is large and transversely furrowed, though not so complex as, for instance, inLamna; the medulla is of some length, though far shorter than in primitive forms. Beyond these more general features, in which this brain occupies a central position among those of Elasmobrauchs, it should be noticed that the olfactory bulbs, although not double as in Carcharias, are very distinctly bilobed. They are united to the cere- brum by short, thick, hollow peduncles. The cerebrum is of the massive type with strongly thickened lamina terminalis, and has upon its dorsal surface two pairs of rounded eminences in place of the single pair noted in Acanthias ; it shows no other external sign of lateral separation. The cerebellum has four main transverse fissures besides a few somewhat more partial and indistinct. The lobi inferiores, hypophysis, and saccus vasculosus are prominent, and very typical in form and arrangement. D. 78. The brain of a Tope {Galeus communis) isolated. The vascular roof has been removed from the rhomboid fossa. 0. C. 1311. Ilunterian, 80 PHYSIOLOGICAL SBRIEI3. D. 79. The brain of a Shark, probably a species of CarcJiarias. The fore-part of this brain agrees in all important particulars with the published descriptions of that of the Blue Shark {Carcharias glaucus). The olfactory bulbs are completely double, each part being attached to the olfactory peduncle by a short separate stalk. The peduncles are long and apparently solid^ and terminate on either side in an oval swelling upon the lateral parts of the cerebrum, far back to wai'ds the ventral surface. The large and massive cere- brum shows no external sign of division upon its dorsal aspect, but beneath there is a slight median furrow. Pos- teriorly it overhangs the thalamencephalon and meets the anterior surface of the optic lobes. In other respects this brain closely resembles that of Galeus. 0. C. 1311 b. D. 80. A specimen of the brain of a Shark, with the medulla removed. It is probable from the general form of the cerebrum, and more particularly from the characteristic method of origin of the olfactory peduncle (seen on the right), that this is the brain of a Carcharias. It is strongly bent artificially towards the ventral aspect, and a piece has been removed from the left side of the cerebrum by trans- verse and sagittal incisions, to show the immense thickness of the dorsal cerebral wall and the relatively small size of the ventricle. Upon the transverse sectional surface, a portion of the choroid plexus can be seen protruding from the ventricular cavity. The method of apposition of the medul- lary auricles in the mid-line can be clearly seen beneath the posterior lobe of the cerebellum. 0. C. 1311 A a. D. 81. The cranium of a Monk-fish {Rhina squatina), with the brain in situ exposed from the dorsal and ventral aspects. The brain in this fish is remarkable for the slight develop- ment of the olfactory centres, for not only are the bulbs and peduncles peculiarly small for an Elasmobranch, but the cerebrum is also feeble. The latter is thin-walled (so that its apparent size is deceptive), with a pair of rounded swellings on its dorsal aspect, and is deeply cleft anteriorly as in some of the lower Sharks. The low type of the braiii is further shown by its long narrow form ; and by the NERVOUS SYSTEM. — VERTEBRATA. gl relatively great development of the medulla, its gradual passage into the cord, and widely open rhomboid fossa. In contrast to the large medulla, the cerebellum is small, its greater part consisting (as in the Eays) of the posterior lobe. Its sides are somewhat swollen to form a pair of lateral lobes (peduncles) close in front of the medullary auricles. The Q])tic lobes are oval and of moderate size ; the lobi inferiores scarcely distinguishable; the hypophysis small; and the saccus vasculosus and infundibulum very large. It should be particularly noticed that the brain combines features characteristic respectively of the Sharks and Rays— the cerebrum and medulla conforming to the former type, the cerebellum to the latter. The brain occupies only a small part of the spacious cranial cavity. RAJIDA. D. 82. The cranium of a Skate (Eaja hatis) with the brain exposed. The brain occupies only a small part of the cranial cavity, and is chiefly remarkable for the strong development of the olfactory centres and for the antero- posterior shortening of the medulla and the prominence of the auricles and lobi linea3 lateralis. The olfactory bulbs are solid and differ considerably in shape from those of Sharks ; each is laterally lengthened and bears a somewhat similar relation to its peduncle that the foot of a stocking does to the leg, the heel being repre- sented by the swelling at the end of the peduncle, and the foot by the part of the bulb that extends outwards alono-the posterior surface of the olfactory capsule. The peduncles are solid and very long; each terminates in a strongly pro- nounced swelling on the lateral surface of the cerebrum. Owing to the presence of these the cerebrum is remarkably broad ; it is convex anteriorly, but has no median groove- upon Its dorsal surface are a pair of indistinct eminences.' The thalamencephalon and mid-brain are well developed but in no way remarkable. The former is somewhat longer and narrower than in many Rays. The optic lobes although dwarfed by the great size of the fore-brain, are m reahty well-doveloped; the lobi inferiores, infundibulum VOL. U, „ ' H2 PHYSIOLOGICAL SERIES. saccus vasculosus, and hypophysis are also strongly marked. The latter is connected (as in other Elasmo- branchs) by a blood-vessel to a transverse bar of vascular connective tissue closely adherent to the perichondrium. The cerebellum differs from that of a Shark in tho slight development of its anterior lobe. Its surface is smooth except for a single transverse furrow and slight lateral indentations. At the sides of the posterior lobe lie the strongly developed auricles and lobi linese lateralis ; the latter apparently owe their size to the peculiarly large nerve- supply necessary for the lateral-line organs and ampullsB. The medulla shows a very high degree of antero-posterior concentration, the rhomboid fossa extending only a short way beyond the cerebellum. D. 83. The brain of a Skate (Raja hatis) dissected to show its internal structure. The dorsal parts of the cerebrum have been removed to show the solidity of its walls and the extremely small size of the ventricle. The latter, although of some little extent in the horizontal plane, is reduced to Fig. 22. Cerebrum of Raja batis (horizontal section). a mere slit dorso-ventrally. Its outline can be traced with difficulty in the specimen ; it is clearest towards the extremities of the lateral ventricles. Behind the cerebrum, the brain has been divided by a mid-sagittal incision and its two halves have been separated. Its internal structure differs in several particulars from NERVOUS SYSTEM. VERTEBRATA. 83 that of Scyllmm (D. 73), the most noteworthy being the relatively small size of the cavities of the optic lobes^ the more massive structure of the cerebellum, and the absence of a cavity in its anterior lobe. Upon the right side, the posterior lobe of the cerebellum has been removed to show the complicated folding of the medullary auricle and its passage into the longitudinal zone of the cerebellum. The olfactory bulbs and the greater part of the peduncles have been removed. Transverse sections of them are mounted above to show that they do not contain a cavity. D. 84. The cranium of a Torpedo {Torpedo galvanii) opened from above to expose the brain. A pair of immense electric lobes form the most striking and important feature of the brain; they are developed in the floor of the medulla, and apparently represent the motor vagal lobes of other Elasmobranchs in a state of excessive hypertrophy. Pro- jecting upwards, they entirely fill and obliterate the rhomboid fossa and are bounded anteriorly by the auricles and cerebellum. Each gives rise to two large bundles of nerves for the electric organ. The electric lobes contain a number of gigantic ganglion-cells, the axis-cylinders of which pass directly into the electric nerves. The brain, with the exception of the electric lobeSj is poorly developed. The cerebellum is very small, diamond-shaped, and, but for a cruciform furrow, smooth. The optic lobes are of moderate size, although the nerves are remarkably slender. The cerebrum is globular, with slight prominences on its dorsal surface ; it receives at its antero-lateral corners a pair of fine solid olfactory peduncles. 0. C. 1310. Hunterian. Rohon, Arb. Zool. Inst. Wien, t. i. 1878, p. 151. HOLOCEPHALI. D. 85. Two specimens of the brain of a Sea-Cat {Chimcera monstrosa). In the lower specimen the brain is seen in situ from above, the hypothalamus and neighbouring parts being also exposed through li window cut in the cranial floor. In the upper specimen the internal structure is shown by G 2 84 PHYSIOLOGICAL SEKIES. the removal of the roof of the thalamoncephalon and the upper part of the left hemisphere, and by the sagittal division of the hinder parts of the brain and the turning to one side of the left half (fig. 23). MED. AUR. OLF. BULB. Brain of Chimcera monstrosa (dissected). The brain is divisible into three well-defined regions : — (i.) A large anterior mass composed of two pairs of con- tiguous lobes, the anterior of which are small and in connection with the olfactory organs, and the posterior united together in the mid-line ; they are the olfactory bulbs and cerebral hemispheres, (ii.) A remarkably long and slender thalamencephalon. (iii.) The mid-brain, cerebellum, and medulla — a considerable mass, remarkable for its great dorso-ventral depth. This hinder part, owing to the resemblance that the sides of the thalamencephalon bear to olfactory peduncles, was formerly supposed to include the cerebrum. A more detailed examination will show that this brain, in spite of its obvious peculiarities, is, apart from the cerebrum, essentially that of an Elasmobranch. The olfactory bulbs are small and rounded in form ; each is feebly bilobed. They arc separated from the hemispheres by a furrow. Each hemisphere is fusiform, and is attached to its fellow near the middle of its median surface by a delicate lamina terminalis continuous above and below with the roof and the floor of the thalamencephalon. Slightly behind the lamina a large semicircular opening (foramen of Monro) leads on each side from the 3rd ventricle into a cavity that NERVOUS SYSTEM. — VERTEBRATA. 85 extends within tlie hemisphere to the olfactory bulb. The posterior part of this cavity is mainly occupied by a prominent swelhng on the lateral wall of the hemisphere, that probably I'epresents the corpus striatum. The thalamencephalon forms a tube 25 mm. long ; its sides are ribbon-like and fairly thick, but the floor and roof are composed only of epithelium and pia mater. The roof is more extensive than the space between the lateral walls and thus bulges upwards, particularly in front, in a sac- like manner. It is infolded in the mid-line in its anterior two-thirds to form a choroid plexus, small processes of which project into the lateral ventricles. At its hinder end it forms a conical projection that accompanies the epi- physis. In front of the epiphysis the roof of the thalamen- cephalon is swollen to form a pair of prominent ganglia habenulse which, as in the Amphibia, form a j^rojecting lip when the tela choroidea is removed (upper specimen). Behind the epiphysis, the anterior border of the optic tectum is thickened to form the posterior commissure. The optic lobes are of considerable size, and contain a large ventricle, the lower half of which is partly filled by a swelling of the lateral walls. The cerebellum is simple, though well developed: it is diamond- shaped, with anterior and posterior lobes each containing an offshoot from the common ventricle; its surface is smooth with the exception of a longitudinal furrow and a feeble transverse indentation. The inner surface of the cerebellum is marked by a pair of prominent longitudinal ridges similar to those of Elasmobranchs, and, like them, continuous with the medullary auricles. The medulla is strongly concentrated antero-posteriorly, and is remarkable for the great development of two pairs of lobes. One pair (lobiis lineaj lateralis) is continuous with the auricles and gives origin on either side to the dorsal root of the ophthalmicus superficialis vil. The second pair (tuberculum acusticum) lie below them, and give rise to the lateralis and the lower roots of the lateral- line branches of the vil. nerve. The lobus vagi is nodulated as in Elasmobranchs. The lobi inferiores, though small, are remarkably prominent. The saccus vasculosus is well- developed. 86 PHYSIOLOGICAL SERIES. F rom the above it will be seen that the hinder part of the brain is closely similar to that of an Elasmobranch, parti- cularly in the conformation of the cerebellum and medulla. The optic lobes show a slight tendency towards the Teleostean type in having an enlargement on their lateral walls suggestive of the torus semicircularis, but the hypothalamus is essentially that of an Elasmobranch. The cerebrum in its relation to the olfactory bulbs, in the considerable separa- tion of the hemispheres and the relative thickness of their dorsal and veutro-lateral walls, is closely similar to that of a Dipnoan or low Amphibian. Wilder, Proc. Ac. Sci. Philad. 1877, p. 219. GANOIDEI. D. 86. Part of the skull of a Sturgeon [Acijoenser sturio) with the brain exposed from the dorsal and ventral aspects. In comparison with the size of the fish (this individual weighed 154 lbs., and measured 6 ft. 4 in.) the central nervous system is peculiarly small. The brain occupies only a part of the spacious cranial cavity, and in its superficial features combines characters found in Elasmobranchs, Amphibia, and Teleostea: for example, the medulla resembles that of a low Shark or Amphibian, whereas the cerebellum is very similar to that of Ceratodus but is provided with a valvula as in Teleosts. Or, again, the mid-brain and thalamencephalon have a strong superficial likeness to those of Ceratodus, whereas the cerebrum resembles that of a Teleostean in having an epithelial pallium. The medulla broadens gradually from the cord towards the cerebellum, and has a very widely-open rhomboid fossa covered by a strongly pleated vascular roof (removed and mounted on the left in the specimen). In its floor are a pair of well-marked fasciculi longitudinales, each of which sends a strong offshoot to the motor root of vii. In the hinder part of the rhomboid fossa on either side lie the sensory vagal lobes, nodulated as in Sharks. To the side and in front of the vagal lobes, the margin of the rhomboid fossa swells to form a conspicuous lobe on either side (lobus linese lateralis) that gives origin to certain nerves of the NERVOUS SYSTEM. — VERTEBRATA. 87 lateral line. In front of the lobus linete lateralis the margins of the rhomboid fossa bend upwards and slightly outwards to form the posterior crura of the cerebellum. The cerebellum forms an upstanding recurved anterior border to the rhomboid fossa. Its anterior parts (not shown in the specimen) project within the optic lobes, forming a valvula cerebelli as in Teleosts. Molecular, nuclear, and intermediate layers are present in the cere- bellum, but, as in Elasmobranchs, the distribution of the nuclear layer is very partial, and Purkinje's cells are irregularly disposed. The optic lobes are very small and, as in Dipnoi and Urodeles, form a single globular enlarge- ment without a distinct median furrow. They are said to contain small tori longitudinales and semicirculares similar to those of Teleosts. The thalamencephalon is narrow and fairly long, with a well-developed hypothalamus. The sides of the infundi- bulum are swollen to form a pair of small lobi inferiores. The saccus vasculosus is well-developed. As in most Elasmobranchs and many Teleostea, the epiphysis is long and thread-like ; towards its base it is in close contact with the roof of a large conical paraphysis. The cerebrum is of relatively small size, and consists of basal ganglia (striatum and epistriatum) covered by an epithelial roof, in which a few nerve-elements have been observed. The olfactory bulbs are sessile on the cerebrum ; each contains a cavity in connection with the cerebral ventricle, and receives a large olfactory nerve indistinctly separable into two bundles. Johnstone, Zool. Jahrb., Bd. xv. 1901, p. 59. TELEOSTEA. Rabl Ruckhard, Arch. Anat. u. Phys. 1898, p. 345 [Pallium). Haller, Morjjh. Jahrb., Bd. xxvi. 1898, p. 632 {Histol, Bihliogr.'). The brain of Bony Fishes differs from that of Elasmobranchs in many important features. It is far more concentrated longi- tudinally, and is remarkable for the strong development of the optic lobes, which in some cases completely dominate the rest of the brain and render it nearly globular in form. On ,88 PHYSIOLOGICAL SERIES. the other hcand the olfactory region, whose great development forms one of the most striking features of the Elasmobranch brain, is peculiarly feeble in the Teleostea. The olfactory bulbs are small, either sessile upon the cerebrum or connected with it by long peduncles, and the cerebrum itself is represented by a pair of rounded basal ganglia roofed over by an epithelial non- nervous pallium (fig. 24). The thalamencephalon shows essentially the same features in both groups, although much compressed antero-posteriorly in the Teleostea. The cerebellum is large, except in some sluggish bottom fish (e. g., Lophius, Cyclopterus), but is usually solid and not hollow as in the Elasmobranchs. Its anterior parts Fig. 24. BL.CORP. ; ^ PALL. BL.Y. Section of Pallium and Corpus striatum of a Gold-fish. also are strongly developed, and protrude forward beneath the tectum opticum into the cavity of the optic lobes, forming the highly chai;acteristic Teleostean valvula cerebelli. The medulla is in most cases much concentrated and often shows remarkably well-developed facial and vagal lobes. The basal ganglia of the cerebrum have much the same minute structure as in Elasmo- • branchs ; they are united by commissural strands (c. interlobu- laris) that occupy a thickening of the floor of the common ventricle. These commissures are derived partly from the olfactory areas and partly from the striatum. Their relation to the anterior commissure of Mammals is doubtful. The thalamencephalon, in minute structure and arrange- ment of tracts and nuclei, is approximately similar to that in Elasmobranchs, the cerebro-hypothalamic tracts being, however, NERVOUS SYSTEM. — VERTEBEATA. 89 specially strong. The tectum opticum has also essentially the same structure in both groups, although its elements are in Teleostea arranged somewhat more definitely in layers. The ependyma and nervous tissue also are greatly developed on either side o£ the mid-dorsal line of the tectum forming a pair of longitudinal ridges (tori longitudinales), traces of which are also found in Eeptiles and Birds. The lateral parts of the optic lobes contain a pair of large nuclei (n. laterales), from which a considerable proportion of the fillet — a particularly well- developed tract in Teleosts — takes its origin. They are super- ficially visible as a pair of bulgings into the cavity of the optic lobes (tori semicirculares). The cerebellum and valvula show the structure common to the cerebellum of all Vertebrates ; Purkinje's cells are, however, somewhat irregularly disposed. The valvula is connected by tracts to the lobi inferiores. ANACANTHINI. D. 87. The cranium of a Cod ( Gadus morrhua) in sagittal section, showing the brain from the left side. The cranial cavity is very extensive, and is only partially occupied by the relatively small brain. The latter shows well the main Teleostean characters. The olfactory bulbs are small round bodies lying close beneath the olfactory capsules; they are con- nected by long delicate tubular peduncles (the ventral parts of which only are nervous) to the basal region of the cere- brum. The peduncles lie close side by side for the posterior two-thirds of their course ; in front they diverge towards the olfactory capsules and gradually increase in calibre. The basal ganglia of the cerebrum form two pronounced swellings of the cerebral floor; they are separated from one another dorsally by a deep sagittal fissure and are ventrally united by a transverse commissure. Each is dis- tinctly lobulated, the two main lobules (striatum and epistriatum) lying respectively antero-lateral and postero- mesial. The roof of the cerebrum (pallium) is entirely non-nervous and consists of a continuation of the ependyma that lines the brain-cavities, in conjunction with the pia mater. In front it is continuous with the epithelial roof of the olfactory tracts, and behind with that of the thalamen- 90 PHYSIOLOGICAL SERIES. cephalon. The dorsal and lateral parts of the thalainen- cephalon are much restricted, being buried to a considerable extent by the optic lobes ; but the hypothalamus is strongly developed, the lobi inferiores in particular being large and prominent : they lie almost directly below the optic lobes. The latter are of great size, of almost globular form, and are separated in the mid-line by a sharp furrow. The optic tracts arise mainly from their superficial parts, and pass forward on either side of the thalamus to the ventral surface of the cerebrum ; here they leave the brain and cross — the right below the left — to form the optic nerves. The cerebellum is tongue-shaped with its free end over- hanging the rhomboid fossa. It is connected with the basal parts of the brain by a pair of prominent anterior crura that give passage to the cerebellar tracts and contain the nuclei of part of the trigemino-facial nerve complex. The medulla, in comparison with that of a Shark, is much concentrated. The rhomboid fossa is consequently small. Its borders show definite swellings, due to the posterior crura of the cerebellum and to the nuclei of the posterior cranial nerves. D. 88. Parts of the head of a Cod {Gadus morrhua) with the brain exposed from the lower surface. The optic nerves, before entering the brain, cross one another, the left beneath the right. Behind this crossing lies the large spherical pituitary body attached to the antero-ventral surface of the infun- dibulum. It covers the anterior parts of the lobi inferiores. Behind it in the mid-line, separating the posterior parts of the lobi inferiores, is a small saccus vasculosus continuous with the distal end of the infundibulum. In this specimen the distribution of the third pair of cranial nerves is shown. It sends branches to the inferior, superior, and internal recti and to the inferior oblique, as well as a ciliary branch to the eyeball. A bristle is placed beneath the branch to the inferior oblique. 0. C. 1380 A. 8. D. 89. A sagittal section of the cranium and brain of a Cod (Gadtis morrhua). Black paper, inserted behind the pallium, brings out clearly the relations of this membrane to the basal NERVOUS SYSTEM. — VERTEBRATA. 91 ganglia and olfactory tracts. At the root of the olfactory tract can be seen the cut edge of the commissura inter- lobularis (fig. 25, ant. comm.). The common cavity of the infundibulum and saccus vasculosus is clearly shown ; in the side wall of the former is a minute opening that leads into the ventricle of the right lobus inferior. At the anterior end o£ the tectum opticum lies the section surface of the small posterior commissure. A narrow passage leads from the aqueduct of Sylvius into the cavity of the optic lobes *. In the section this cavity is largely obliterated by one of a pair of longitudinal ridges (tori longitudinales) that lie on either side of the mid-dorsal Fig. 25. TECT. OPT. AQ. SYL. CER. ANT. COMM. FOR.LQB. INF. VALV.CER. Braiu of Gadus morrhua in sagittal section. line of the tectum. The torus is thickest anteriorly where it abuts on the posterior commissure, and gradually fades away posteriorly. The hinder part of the optic ventricle is occupied by a forvvardly projecting process of the cerebellum (valvula cerebelli) . This structure is formed by the invagination of the anterior parts of the cerebellum into the cavity of the mid-brain, and thus in sagittal section shows two superposed layers — the lower one continuous behind with the cere- bellum and passing in front by reduplication into the dorsal layer. The latter is closely applied to the first, and is continuous posteriorly with the hinder margin of the tectum opticum. Beneath the posterior lobe of the cerebellum can * la iig. 25 the leading line fromAQ.SYi,. points somewhat too far back. 92 PHYSIOLOGICAL SERIES. be seen the out surface of the nervous bridge thiit unites the two posterior crura of the cerebellum, and behind this the lobus facialis and lobus vagi. 0. C. 1308 0. D. 90. A similar specimen in which the structure of the optic lobes and valvula cerebelli is more clearly visible. In this specimen the left optic nerve crosses above the right. D. 91. The brain of a Cod ( Gadus morrhtid) dissected from above. The posterior lobe of the cerebellum and the tectum opticum with the exception of the torus longitudinalis have been removed, thus exposing the medulla and the cavity of the mid-brain. Within the optic ventricle are certain marked prominences : on either side a large semi- lunar excrescence (torus semicircularis) due to the presence at this spot within the latere- ventral walls of the mid-brain of a nucleus in connection with the fillet : in the central mid-line at the hinder end of the ventricle a subconical projection (valvula cerebelli), the structure and relations of which are shown in the previous specimens : and in the dorsal mid-line a pointed tongue-like process that extends from the posterior commissure to the hinder end of the tectum opticum. This structure, composed of the two tori longitudinales, consists of nerve elements and a local thickening of the ependyma that lines the brain-cavities. Beneath its broad anterior end lies the narrow opening by which the optic ventricle communicates with the aqueduct of Sylvius. The dorsal surface of the medulla is occupied by a series of swellings that almost entirely close the rhomboid fossa, and are due mainly to the sensory nuclei of the cranial nerves (fig. 26). Judging by Goronowitsch's account of these structures in Lota, their relation to tlie several cranial nerves should be approximately as follows : — The prominent lateral crura of the cerebellum contain besides cerebellar tracts, a pair of large nuclei from which arise the acoustic and lateral-line nerves. These lobes apparently represent the tuberculum acusticum of Klasmobrauchs (Johnstone, Zool. Jahrb. 1901, p. 159) or the Sturgeon shifted forward owing to the concentration of the medulla. Close behind NERVOUS SYSTEM. — VERTEBRATA. 93 the cerebellum and exposed by the removal of its free extremity, are a pair of prominent lobes (posterior crura of cerebellum) ; they are united above the fourth ventricle by a commissure, but otherwise are very similar in aspect to the lobi linese lateralis of Elasmobranchs. They must, however, be compared with the medullary auricles as they consist entirely of a backward prolongation of the cere- bellum. Behind these, on a level with the exit of the Fig. 26. Brain of Gadus morrhua (dissected). vagus from the brain^ are a pair of lobes almost contiguous in the mid-line suid each indistinctly divided by a longi- tudinal furrow. They give origin to the sensory roots of the facial and glosso-pharyngeal and represent a dis- membered portion of the lobus vagi of lillasmobranchs. Behind and to the sides of these lobes are elongated and somewhat irregular excrescences from which arise the sensory roots of the vagus. Goronowitsch, Festschr. fiir Gegenbaur, Bd. iii. 1897, p. 14 [Lota). 94 PHYSIOLOGICAL SERIES. D. 92. The brain of a Bib {Oadus lusms) exposed from the left and ventral aspects. In comparison with the brain of the (;od, there are noticeable differences in the relative proportions of the parts — the cerebral basal ganglia and optic lobes being much more nearly equal in size. This is due partly to an increase in the size of the basal ganglia, and partly to a decrease in the optic lobes relative to the brain as a whole. The right optic nerve crosses below the left. The saccus vasculosus is more prominent than in the Cod, and the pituitary body very much smaller. The lobi inferiores meet in the mid-line behind the saccus vasculosus. 0. C. 1380 A 5. D. 93. The head of a Five-bearded Rockling {Motella mustela) with the ventral surface of the brain exposed. The optic nerves cross — the right below the left — at a considerable distance in front of the brain. In this specimen parts of the trigeminal nerve are also shown. 0. C. 1380 A 7. D. 94. The head of a Sole (Solea vulgaris) with the brain exposed. Owing to the torsion of the skull the fore part of the brain is rotated to the right, but the region behind the optic lobes is quite similar to that of other fishes except for a hardly perceptible tendency to bend towards the right. The medulla is fairly long, with a pair of very prominent lobes (facial ?) upon its dorsal surface. The cerebellum is small, nearly globular in shape, and projects slightly back- wards over the rhomboid fossa. The optic lobes are also of moderate dimensions, and give off equal-sized optic nerves. The left nerve passes above the right and twists round above the sphenoid bone to reach the left eye which is displaced to the right side of the fish. The thalamencephalon is remarkably elongated for a Teleostean, and forms a conspicuous neck between the optic lobes and corpora striata. The olfactory bulbs are large and are separated from the basal ganglia by a considerable constriction. The parts NERVOUS SYSTBM. — VBRTEBRATA. 95 of the fore-brain show a distinct tendency towards a linear arrangement, the olfactory bulb and corpus striatum of the left side being thrust to a marked degree behind the corre- sponding parts on the right. The lobi inferiores are globular and prominent. D. 95. The head of a Brill {Rhombus Icevis) with the brain exposed from the right (blind) side. The brain is perfectly sym- metrical. The optic lobes are relatively somewhat larger than in the Sole. The corpora striata are very small, with sessile olfactory bulbs at their anterior end. The left optic nerve passes below the right. 0. C. 1380 A ii. D. 96. A similar specimen of the brain of a Hallibut {Hippoglossus vulgaris) exposed from the right (ocular) side. It closely resembles that of the Brill except for its larger size. ' The mfundibulum and saccus vasculosus are very prominent. The right optic nerve is slightly smaller than the left, it crosses beneath it ; both are of immense size. ACANTHOPTBRYGII. D. 97. Fart of the cranium of a Gilt-Head {Chrysophrys aurata) with the brain exposed from the right side. The small olfactory bulbs are sessile on the cerebrum ; each gives rise to a stout olfactory nerve. The basal ganglia are immensely developed ; each is a lobulated globular body slightly larger than one of the optic lobes. The latter are of moderate dimensions ; the lobi inferiores are large and longitudinally elongated. The cerebellum is small, quadri- lateral in outline, and of considerable dorso-ventral depth. The right optic nerve crosses beneath the left ; its distal part has been opened out to show its flat ribbon-like form and pleated folding. 0. C. 1380 A 20. D. 98. The brain of a Mackerel {Scomber scombrus) exposed from the right and dorsal aspects. The olfactory bulbs and corpora striata are small and closely contiguous, form- ing together a pyramidal anterior extremity to the brain. The lobi inferiores are small, but the optic lobes are of 96 PHYSIOLOGICAL SERIES. remarkable size, pressing in front against the corpora striata and overhung posteriorly by the cerebellum ; tliev are globular in shape, separated in the mid-dorsal line by n shallow groove. Upon the antero-lateral surface of each is an indentation from which emerges the main part of the optic tract. The lobule that lies postero-ventral to Ihe indentation is due to an overlapping of the tectum opticum. The right optic nerve crosses below the left ; both are of great size, although the eyes in this fish are comparatively small. The cerebellum is of moderate size ; it is egg- shaped, with its narrow end projecting forwards over the hinder half of the optic lobes. The crura cerebelli are strongly pronounced. The medulla is much shortened antero-posteriorly. 0. C. 1380 A i8. D. 99. The cranium of a Mackerel (Scomber scomhrus) with the brain exposed from above. The roof of the optic lobes and the anterior free end of the cerebellum have been removed to show the valvula cerebelli. This organ occupies the Fig. 27. Valvula cerebelli of Scomber scombrus, major part of the cavity of the optic lobes and is to a great extent responsible for their size. It consists of a central lobe directly continuous with the cerebellum, and of two lateral lobes or wings formed by the reduplication of the anterior ends of the central lobe. This relation of the lobes to each other is shown in the diagram (fig. 27). D. 100. The skull of a Fishing-Frog {Lopldm piscatorius) with the brain exposed from the dorsal and ventral aspects, and with the origins, and in some cases the peripheral parts, of the cranial nerves shown. NBKVOUS SYSTEM. — VERTEBRATA. 97 The brain is feebly developed and occupies only a small part of the spacious cranial cavity. The fore-brain is re- markably small ; it forms a pyramidal eminence in front of the optic lobes. The bulbi olfactorii are sessile on the basal ganglia, but in this specimen are hardly to be distin- guished. They give oflP delicate olfactory nerves. The optic lobes are large in comparison with the feeble development of the rest of the brain, but are not in reahty particularly strong. They are separated in the mid-dorsal line by a shallow groove. The cerebellum is extremely small for a Teleostean, forming merely a little rounded excrescence between the hinder margins of the optic lobes. The medulla is followed by a swollen region of the cord with a single pair of eminences upon its dorsal surface. This enlargement is by some included in the medulla, and homologized with the vagal lobes, but from its micro- scopic character (Ussow, Arch. Biol. t. iii. p. 642) it seems that it more likely is a modified part of the cord, comparable to the metameric swellings found in this region in the G-urnard. It should be noticed that in both cases the anterior spinal nerves are strongly developed. The pituitary body is a remarkable structure both for its enormous size and its position a centimetre or more in front of the brain. It is spherical and connected to the infundibulum by a long delicate pedicle. The pineal gland is situated in a similar way beneath the cranial roof far in front of its point of origin upon the roof of the thalamencephalon. The same forward shifting is noticeable to a less degree in the eyes, in the position of the optic chiasma, and in the point of exit from the brain of the trigeminal complex of nerves. Possibly in all cases it is due to the great development of the anterior face-region. The lobi inferiores are peculiarly small ; they lie one on either side of a prominent saccus vasculosus. In this specimen the spinal cord is also shown (for description see D. 754). 0. C. 1308 n. D. 101. The isolated brain of a Fishing-Frog {Lophius pisca- torius). This specimen shows the features mentioned in VOL. n. H 98 PHYSIOLOOICAL SKRIES. the description of the previous specimen, but with greater clearness. The pedicle of the pituitary body is nearly 20 mm. long. 0. C. 1308 m. D. 102. The brain of a Guru;ird {Trlgla hirundo) exposed in situ from above. The olfactory bulbs are of some size ; they are sessile on the cerebrum, aud each gives origin to a stout olfactory nerve. The basal ganglia are glolnilar, smooth, and very large ; the optic lobes are also well developed and somewhat flattened antero-posteriorly. The small cerebellum projects slightly backwards; it has prominent crura. The medulla is short, with well marked vagal lobes on either side of the rhomboid fossa. The anterior part of the cord is much thickened, and shows upon its dorsal surface a series of 5 pairs of metameric enlargements, which are fully described in the section devoted to the spinal cord. 0. C. 1308 H. D. 103. A young Lump-Fish {Cydopterus lumjms), 3*5 cm. long, with the brain and spinal cord exposed from above. The brain is similar in all essentials to that of the adult, but is shorter and broader in outhne, larger relatively to the size of the body, and more nearly fills the cranial cavity. The latter feature is common to the young of many Teleosts. 0. C. 1308 L a. D. 104. The head of a Lump-Fish {Cydopterus lumpus) with the brain exposed from the dorsal and ventral aspects. The brain is poorly developed in every part. The minute olfactory bulbs are sessile upon the cerebrum. The optic lobes are oval in outline, and, although they form the largest region of the brain, are very small in comparison with those of most other Teleosteans. The cerebellum hangs backwards over the front part of the rhomboid fossa; it is oval, quite small, and without prominent crura. The medulla is remarkably long and narrow, and merges gradually into the cord much as in the lower Sharks. It shows no definite superficial eminences, and no doubt owes its simple unmodified character to the peculiarly feeble development of the cranial nerves. Presented hy W. B. Tegetmeier, Esg. NERVOUS SYSTEM. — VERTEBRATA. 99 D. 105. A Dragonet {Callionymus lyra) with the brain and spinal cord exposed from above. The optic lobes are very strongly developed. The cerebellum very closely resembles that of LopUus ; it is a small rounded eminence lodged between the hindei- margins of the optic lobes, and protrudes slightly over the rhomboid fossa. The medulla is small and shows no clear separation from the cord. In this specimen the corpora striata have been removed. 0. C. 1308 I. PHARTNGOGNATHI. D. 106. The head of a Wrasse {Labrus sp.) with the brain shown in situ from above. The brain occupies the greater part of the cranial cavity. It is remarkable for the great development of the basal ganglia, which equal, if they do not exceed, the optic lobes in size. Each is roughly triangular when seen from above, and is contiguous in the mid-line with its fellow by one of its sides. Their surface is distinctly lobulated. The cerebellum is tongue-shaped ; its greater part hangs backwards over the rhomboid fossa but there is also a small anterior lobe. Its surface is crinkled, probably by shrinkage. The crura cerebelH are well-marked. 0. C. 1308 Q. PHYSOSTOMI. Mayser, Zeits. wiss. Zool. Bd. xxxvi. 1882, p. 259. D. 107, The brain of a Carp (Cyprinus carpio) shown in situ from above (fig. 28) . In the Carp family the brain is distin- guished by the great development of the vagal and facial lobes. This development renders the medulla unusually broad and defines it abruptly from the cord. The vagal lobes form a pair of large wing-like swellings on either side of the rhomboid fossa, and embrace between their anterior ends the unpaired facial lobe— a rounded body situated in the dorsal mid-lino behind the cerebellum. This ''lobus impar" represents apparently a fusion of the two small facial lobes seen in the Cod (Goronowitch, I.e. p. 23). The cerebellum, though much elevated, is of moderate size ; it hangs slightly backwards over the medulla. The optic lobes are superficially very large, but h2 100 PHYSIOLOGIOAL SERIES. owe their size mainly to the great development of the valvula cerebelli. Their roof is composed as usual of two chief layers — an outer cellular and fibrous layer from which the optic tracts arise, and an inner commissural layer; but the outer layer is deficient over a large triangular area in the mid-dorsal parts, leaving a semitransparent membrane (the commissural layer) through which the wings of the valvula cerebelli can be seen (upon the right Fig. 28. CUT EDGE. LOB. FAC. CORP.STR. /'■ CER. / LOB-VAG. ^•OLF. BULB. tPIPH: ,i VALV. CER, TECT. OPT. Brain of Cypnnus carpio. side black paper has been inserted beneath a part of this exposed commissural layer). The epiphysis is small and pear-shaped. The olfactory bulbs are situated close to the olfactory organs. The olfactory peduncles are somewhat widely separate, but are connected, as far as the bulbs, both dorsally and ventrally by a delicate membrane (black paper is inserted beneath its anterior end), the upper layer of which is a forward extension of the pallium. D. 108. The head of a Tench ( Tinea vulgaris) exposed from above. This brain has the same general characters as that of the Carp, but differs from it in the smaller size and more globular form of the cerebellum. The tectum opticum also has only a small median area deficient in the outer layer, from which — as this deficiency is apparently due to the thrusting aside of the lateral parts of the tectum by the contained valvula cerebelli — one may infer that the valvula is less developed. Presented by T. W. II. Burne, Esq. D. 109. The isolated brain of a smaller Tench {Tinea vulgaris) . This specimen is similar to the last, but, in addition, shows NERVOUS SYSTEM. — VERTEBKATA. 101 the crossing o£ the optic nerves — the left below the right — as well as the union of the lobi inferiores in the mid-line behind the saccus vasculosus. The olfactory bulbs and peduncles have been removed. 0. C. 1380 A 15. D. 110. The head of a Barbel {Barbus vulgaris) with the brain exposed from above. The cerebellum is considerably larger than in the Tench; it is oblong and overhangs the anterior part of the medulla. The optic lobes are well-developed. In the mid-line the outer layers of the tectum are deficient, exposing a transparent commissural area of triangular outline through which the valvula cerebelli is indistinctly visible as in the Carp. The left basal ganglion has been removed, exposing the short thalamencephalon with the ganglia habenulse — two small whitish excrescences on the dorsal margins of the thalamus. The crossing of the optic nerves — the left above the right— can also be seen. From the anterior end of the corpora striata delicate olfactory peduncles are given off. The olfactory bulbs in this and other Carps lie close to the olfactory capsules : they are not shown. 0. C. 1308 B. D. 111. Brain of a Bleak [Alburnus alburnus). It closely re- sembles that of the Tench (D. 108), except in the somewhat smaller relative size of the " lobus impar.^^ D, 112. The brain of a Roach [Leuciscus rutilus) exposed from above. The " lobus impar " and lobi vagi, though dis- tinctly visible, are far less developed than in the other specimens of Cyprinoid brains. Presented by Mr. S. Epprett. D. 113. The head of a Pike [Esox lucius) with the brain exposed from above. For that of a Teleostean, the brain is long and narrow, with tapering medulla and open rhomboid fossa. The cerebellum and optic lobes are considerably developed, the latter having a long oval shape. The epiphysis is saccular and pear-shaped ; it overhangs the small basal ganglia and extends forward to the anterior extremity of the olfactory bulbs, which are sessile on the cerebrum. 102 PHYSIOLOGICAL SERIES. D. 114. The head of Mormyrus juhelini with the brain exposed from the left side. In the Mormyridfe the brain is re- markable for the immense development o£ the valvula cerebelli. This organ does not lie as in other Teleosts completely within the optic lobes, but projects through the tectum opticimi, thrusting its lateral parts downwards to either side, and spreads out in three pairs of lobes or wings over the surface of the brain, completely concealing it from view when looked at from above, and extending so far down on either side as to leave exposed only the lower parts of the hemispheres and optic lobes. This unusual relation of the valvula cerebelli to the tectum opticum appears to be a further extension of some such process as that seen in the Carp (D. 107), in which the lateral parts of the tectum are divaricated and the central area much thinned out, but without extrusion of the valvula. The wings of the valvula are called from their position anterior, lateral or middle, and posterior. Their deep surface is occupied by a layer of small cells (nuclear layer) covered superficially by a number of parallel ridges each composed of molecular, nuclear, intermediate, and fibrous layers. In the specimen the exposed surface of the posterior wings has a finely corrugated appearance due to these ridges, but the anterior and lateral wings are smooth, because, by folding, the deep nuclear layer has become superficial in position. The olfactory bulbs are small and are situated close to the olfactory organs. They are connected by delicate peduncles to the cerebrum. The left basal ganglion can be seen below the anterior wing of the valvula ; it has a somewhat oblong shape. Close behind it, below the anterior part of the lateral wing of the valvula, lie two narrow masses of brain-substance. The anterior of the two is the laterally depressed left half of the tectum opticum ; the other is part of the torus semicii'cularis. Presented by J. S. Bvdgetl, Esq. D. 115. The brain of Mormyrus hannvme exposed in situ from above. The wings of the valvula cerebelli have been re- moved from the left side to exjjose the underlying })arts of the brain. NE U VOUS S YSTEM . — VERTEBRATA. 103 The basal ganglion is well developed and is clearly divided into two lobes, an outer and anterior, and a median and posterior — the striatum and epistriatum. The cavity of the optic lobe is bounded in front by the displaced tectum opticum and is occupied by the large torus semi- circularis. Fio-. 29. • OLF. BULB U3B. IMPAR.-"^ Bi-ain of Mormyrus kannume. The cerebellum is small and tongue-shaped, with its pointed apex directed forwards. Its base is separated in front by a transverse groove from a small rounded emi- nence— the posterior part of the root of the valvula. Behind, a similar but shallower groove divides it from a small lobe (fig. 29, X.) said to resemble in microscopical features the 104 PHYSIOLOGICAL SKUIKS. lobns impai* of the medulla, although superficially it apparently forms pai't of the cerebellum. The medulla is remarkable for the immense development of a lobe upon its lateral and dorsal parts. This lobe (lobus impar) probably represents a fusion of a large median facial lobe, such as that seen in the Carps, w ith a pair of vagal lobes. The latter envelope the sides of the facial lobe and bound with their upper swollen borders a depressed central area — the median parts of the facial lobe. Presented hy G. A. Boulenger, Esq, Saunders, Phil. Trans, vol. clxxiii. 1882, p. i)27. D. 116. The brain of a Herring (Clupea harengus) shown in situ from above. It is remarkable for the great size of the optic lobes and the shortness of the medulla. The optic lobes are oval with a slight lateral depression about the middle. The outer layers of the tectum are deficient in the mid- line at the posterior end, leaving a small triangular area of commissural fibres exposed. The basal ganglia are very closely applied to one another in the mid-line, forming an apparently single globular mass ; they are continuous anteriorly with a pair of conical olfactory bulbs. The cerebellum is oblong and very deep from above downwards. The medulla is mncli concentrated, and has a well-marked facial lobe behind the cerebellum. 0. C. 1308 c. D. 117. The fore part of an Eel {Angnilla vulgaris) with the brain exposed from the dorsal aspect. In front of the medulla the several regions of the brain are of approxi- mately equal size, and as each is more or less clearly bilobed, the brain appears to consist of four pairs of rounded equal-sized nodules situated one behind the other. The anterior pair (olfactory bulbs) are slightly pointed in front and give off two large olfactory nerves. The optic lobes and cerebellum are divided down the middle by a shallow groove. The cerebellum is considerably broader than long, with its anterior and posterior borders parallel. The medulla is small and much shortened. D.118. The head of a Conger Eel {Conger vulgaris) with the brain exposed from above. The brain is moie elongated NERYOUS SYSTEM. — VERTEBRATA. 105 than in Anguilla. It is remarkable for the large size of its olfactory centres and the linear arrangement of its several parts. It also shows a very decided right-handed rotation of its anterior end. The olfactory bulbs are of great size and are separated from the cerebrum by short peduncles. Each receives an immense nerve from the olfactory organ. The right bulb lies partly below the left, much as in the Sole. The basal ganglia of the cerebrum are considerably lobulated, and with the olfactory peduncles can be seen to be covered by a relatively close-fitting pallium. The thalamencephalon is remarkably long for a Teleostean, forming a narrow neck between the cerebrum and the moderately developed optic lobes. The cerebellum is quadrilateral with a marked longitudinal groove on either side. The medulla is small and much concentrated. The fish from which this specimen was made measured 5 ft. 7 in. in length. PLECTOGNATHI. D. 119. A Globe Fish {Biodon sp.) opened along the dorsal surface to show the brain and spinal cord. The brain lies in a capacious cranial cavity, and in dorsal view has an outline very similar to the conventional club on a playing card ; this is due mainly to the great development of the optic lobes. The basal ganglia are also large ; each is distinctly divided by a furrow into a lateral and a median lobe. The olfactory bulbs are not shown. The cerebellum is oblong and overhangs the medulla and anterior part of the cord. The spinal cord is remarkably short, ending in a fine filament less than 10 mm. behind the posterior border of the cerebellum. The remainder of the neural canal is occupied by a cauda equina, indicated on a level with the pectoral fins by black paper. 0. C. 1308 K. DIPNOI. D.120. Parts of the skull of Ceratodus forsteri with the brain exposed. in most characters the brain is very primitive and closely 106 PHYSIOLOGICAL SERIEK. resembles that of a Urodele Amphiljian. It is^ ibr instance, very long and narrow, with spacious ventricles enclosed by thin or, in parts, epithelial walls. The medidla is very like that of a low Shark — long, antl very broad in front with a widely open rhomboid fossa and well marked medullary auricles. It gradually merges into the cord behind. The highest development is shown by the cerebral hemispheres, which are large, like those of Amphibia, and greatly expanded in their ventral parts. They are separated from one another in the mid-line as far back as the anterior commissure. Their walls are thin and even purely epithelial in their dorso-median parts, where they are closely attached to a large glandular paraphysis that projects from the roof of the thalamencephalon wedge- like between them. In front, the lateral ventricles are continued by a narrow passage into the cavities of a pair of strong olfactory bulbs. In the possession of definite olfactory bulbs Ceratodus differs markedly from Protopterus or the Amphibia, and shows more resemblance to Elasmo- branchs. A window has been cut in the left hemisphere and olfactory bulb to show the continuity of their cavities and the relation of the glandular paraphysis to the mesial wall of the hemisphere. The thalamencephalon ar.d mesencephalon, as in Urodeles, are very long and narrow. The former shows a pair of strongly marked ganglia habenula3. The epiphysis, which is not shown in the specimen, is small. The optic lobes form a single prominence of small size between the thalamencephalon and the cerebellum. It is narrower in front than behind, and is divided mesially by a conspicuous but narrow dark band due to a local thinning of the roof. The cerebellum is slightly damaged ; it is more strongly developed than in Amphibia, though less so than in Fishes, and forms a broad transverse band behind the optic lobes, continuous laterally with the medullary auricles. In the floor of the fourth ventricle lie a pair of small fasciculi longitudinales posteriores, and in the lateral walls, rather far back, a pair of longitudinal ridges— the vagal lobes, which in position resemble those of Sharks but are without their characteristic nodulation. NERVOUS SYSTEM. — VERTEBKATA. 107 The epithelial roof o£ the rhomboid fossa is much pleated ; it has been longitudinally bisected and turned to either side. Upon the lower surface of the bniin, the great ventral expansion of the hemispheres and their clearly defined median separation can be seen. The hypophysis has been removed and mounted on the left, thus uncovering the large funnel-like infundibulum. In this specimen the olfactory organs are also shown. On the left, the floor of the narial chamber has been removed to show the transversely pleated character of the roof. A red rod has been itiserted into the anterior and posterior nares on the right. 0. C. 1309 B. Saunders, Ann. Mag. Nat. Hist. ser. 6, vol. iii. 1889, p. 157. D.121. The brain of a Mud-fish {Protopteras annectens) . It chiefly differs from that of Ceratodus in being shorter and more compact, in the absence of separate olfactory bulbs, and in the feeble development of the cerebellum. In all these features it also more nearly resembles the brain of an Amphibian. The cerebral hemispheres are remarkably deep dorso- ventrally, they are united at their posterior end by an anterior commissure situated in the lamina terminalis (this is not shown). In front of the gangha habenulse the epithelial roof of the thalamencephalon is prolonged forwards as a conical paraphysis. The medulla is shorter than in Ceratodus, with the borders of the rhomboid fossa sw^ollen and, half way between the calamus scriptorius and the cerebellum, curved inwards towards the mid-line. There are no de- finite lobi inferiores, but they are possibly represented by the slightly swollen lateral walls of the infundibulum. Burckhardt, Centralnervensystem v. Protopterus, Berlin, 1892. AMPHIBIA. Osborn, Jour. Morph. vol. ii. 1889, p. 51. In the Amphibia, and especially among the Urodeles, the brain is of a remarkably low typo and closely resembles that of a Dipnoan. 108 PHYSIOLOGICAL SERIES. With the exception of the medulla and cerebrum, all parts are veiy poox'ly developed. The medulla is similar in form to that of a low Shark, with wide open fossa rhomboidalis and no sharp boundary towards the cord. The hemispheres, in- cluding the olfactory bulbs which are at the best only slightly indicated, form the largest part of the brain, and show signs of incipient pseudo-occipital lobes. But their size is somewhat deceptive, as the walls are relatively thin throughout. They consist of an outer molecular and an inner cellular layer, and show no signs of cortical formation, unless possibly a small aggregation of cells in the outer layer of the median wall should be regarded as a rudimentary hippocampal cortex. The hemispheres are united by an anterior commissure, in which two portions can be distinguished: one between the basal parts — the true anterior commissure; and the other connecting the olfactory regions of the pallium — a hippocampal commissure. The hemispheres are connected to the thalamencephalon by a large basal tract on either side. The ganglia habenulse are always well marked and externally visible, though not so strong as in the Cyclostomi and Dipnoi. The pineal gland is ves- tigeal. The optic lobes are only developed to any extent in the Anura, and in them have a many-layered tectum. The roof nucleus, in connection with the trigeminal nerve, is particularly strong in Urodeles. The cerebellum, although small, is com- posed of three layers — nuclear, intermediate and molecular, but an internal fibrous layer, owing to the small size of the cerebellar tracts, is not differentiated. UEODELA. D. 122. A Menopoma (Menoponia alleghaniensis) with the brain and spinal cord exposed from above. This specimen, although somewhat damaged, shows clearly the chief superficial cha- racters of the Urodele brain. The cerebral hemispheres are separate in the mid-line nearly to their posterior extremities. Each is large and oval in shape, and projects backwards to some exent over the lateral parts of the thalamencephalon, forming a rudimentary pseudo-occipital lobe. Independent olfactory bulbs are absent, but two strong double olfac- tory nerves arise from the antero- ventral parts of each hemisphere. NERVOUS SYSTEM, VERTEBRATA. 109 Thethalamencephalon and mesencephalon differ little from one another in diameter, and form together a narrow cylin- drical neck between the hemispheres and the broad anterior end of the medulla. A large hole between the hinder extre- mities of the hemispheres indicates the spot from which the conical vascular paraphysis has been removed ; its posterior border is formed by two slight thickenings, the ganglia and commissura habenulfe. The optic lobes are very weak, and do not dift'er materially from those of Protopterus. The cerebellum is quite rudimentary — a mere narrow band of nervous tissue forming the anterior border of the rhomboid fossa. The medulla is flattened from above downwards. In front it is broad, but gradually narrows posteriorly, and merges imperceptibly into the cord. Its lateral walls diverge widely in front and bound an extensive rhomboid fossa. 0. C. 1311 F. ' D. 123. The head of a larval Axolotl {Amhlystoma tigrinurti) showing the brain. It differs little from that of Meno- poma except for the stronger development of the optic lobes. In this specimen the paraphysis and ganglia habenulas are very clear. Stieda, Zeits. wiss. Zool., Bd. xxv. 1875, p. 285. D. 124. A Menohranclms lateralis with the brain exposed from above. It agrees in all essentials with that of Menopoma. 0. C. 1311b. D. 125. The head of a Proteus anguinus showing the brain. The olfactory bulbs are separated from the hemispheres by a slight constriction. The ganglia habenulse are remarkably large ; close behind them lies the minute epiphysis. The optic lobes, as might be expected in a blind creature, are scarcely differentiated, ANURA. D, 126, The head of a Bull Frog {Rana cateshiana) with the brain exposed from above. This brain, though formed on a similar plan to that of a Urodele, differs from it in the relatively greater breadth no PHYSIOLOGICAL SERIES. of the thalamencephalon, in the larger size of the optic lobes, and in the stronger development of the cerebellum. The olfactory bulbs are separated from the hemisf)heres by a shallow constriction and are fused together in the mid- line. Behind this union the hemispheres are separate as far back as the anterior commissure. Between their posterior extremities there is, in the specimen, an oval aperture in the roof of the thalamencephalon caused by tlie removal of the paraphysis ; its hinder margin is formed by the slightly protuberant ganglia habenulas and their commissure. The optic lobes form the broadest part of the brain. They are prominent oval bodies separated in the mid-line by a deep gutter. In front they diverge and expose a part of the tectal commissure. Between this and the thalamencephalon is a small cresceutic pit at the base of which lies the posterior commissure. A deep furrow sepa- rates the optic lobes from the cerebellum. The medulla is somewhat shorter than in the Urodeles. The epithelial and vascular roof of the rhomboid fossa has been removed and mounted at the side to show its pleated under surface. Ecker, Anat. of the Frog (Engl, trans.), 1889, p. 141. EEPTILIA. Edinger, Senckenberg. naturf. Gesell., Bd. xix. 1896 {Cere- brum) &Bd. xxii. 1899 {Thalmnencejyhaloji) . Haller, Morph. Jahrb., Bd. xxviii. 1900, p. 252. The Reptilian brain is narrow and of considerable length, with moderately developed optic lobes and, except in swimming forms with insignificant cerebellum. The medulla oblongata shows'astronglongitudinal dorso-ventral curvature, convex below. In this class the brain differs most markedly from that of a lower Vertebrate in the great structural advance of the cerebrum, notably in the presence, for the first time in the Vertebrate series of an undoubted cerebral cortex (hg. 60) . The condition of the'pallium is of special in.portance. It is not only much larger than that of an Amphibian, but is also much more highly KERVOUS SYSTEM. — VERTEBRATA. Ill differentiated. The mesial wall of the hemisphere is composed of a large dorsal area — the hippocampus, and a ventral spindle- shaped area — the tuberculum olfactorium (see fig. 31). A re- latively narrow strip of thick ganglionic matter extending from the lamina terminalis behind to the olfactory peduncle in front separates these two areas ; this body may be called para- terminal, because its most distinctive feature in the adult is that it lies alongside the lamina terminalis, and in the foetal brain is developed from those parts of the walls of the neural tube which are placed alongside the end or terminal plate. Its Fig. 30. NEUROP. - CORTEX . -- NEUROP. Section of pallium of Tropidonotus natrix, X 150. surface forms the precommissural area, and in Mammals its upper part becomes stretched and otherwise modified to form the septum lucidum {vide Journ. of Anat. & Phys. vol. xxsii. p. 411). In Reptiles and Monotremes the peculiar cortex, of which the tuberculum olfactorium is formed in Meta- and Eutherian mammals, although present^ is ill-defined ; so that the corpus striatum seems to extend to the surface of the ventral half of the brain. A comparison with the condition found in the Monotremes [vide infra) and in the foetal state of all mammals, clearly demonstrates that the whole of the mesial surface of the cerebral hemisphere of the reptilian brain, which is not precommissural area nor tuberculum olfactorium, represents and is homologous 112 PHYSIOLOGIOAL SERIES. with the hippocampus of the mammalian brain (figs. 31, 32, & 33). This hippocampal formation also extends beyond the dorso-mesial edge of the hemisphere, and forms in different reptiles and birds a variable area of the dorsal surface (see " Further Observations on the Fornix," Journ. Anat. & Phys. vol. xxxii. p. 245). The hippocampal formation presents a very different appear- ance to its mammalian homologue because that peculiar modifi- cation of the edge of the hippocampus which in Mammals produces the fascia dentata, has not yet occurred in the Sauropsida, although in many Sauria the first stage in the development of the fascia dentata, viz., a formation of numerous small cells at the ventral edge of the flat hippocampal plate, is distinctly recognizable. Two simple rounded commissures are placed close together in the lamina terminalis. The dorsal of these represents the psalterium of Mammals, being derived from the hippocampus. In many Reptiles such as Sphenodon and the Lacertilia, the caudal half of this commissure is separated from the rest and crosses the middle line not in the lamina terminalis but in a fold of the roof between the paraphysis and dorsal sac. This "com- missura aberrans hippocampi " (usually known by the misleading title <'commissura pallii posterior") is probably a modified in- heritance from the Amphibia, in which certain fibres from the caudal part of the cerebral hemisphere cross the mesial plane along with the fibres of the superior commissure (commissura habenulsej. That part of the pallium which forms the bulk of the whole nervous system in Mammals is represented in Reptiles by a small insignificant area on the dorso-lateral aspect of the hemisphere, which is not sharply differentiated from the pyri- form lobe below it. The neopallium (as 1 have called this part of the pallium [Journ. Anat. & Phys. vol. xxxv. 1901, p. 431]) is so poorly developed that the fibre-systems to which it gives rise— internal capsule, pes pedunculi, and pyramidal system, are absent in the reptilian brain. The chief cerebral tracts are in connection with the olfactory centres, and include some between the olfactory areas and the hippocampal cortex that are of special importance, as they are the first cortico-sensory connec tions to appear in the Vertebrate series. NERVOUS SYSTEM. — VEKTBBRATA. 113 Tn the thalamencephalon the tracts and nuclei are larger and more numerous than in lower forms, indicating a greater com- plexity of connection between the fore and hind parts of the brain, due mainly to the presence of cortical tracts. The nuclei rotundi, in which the main part of the strio-thalamic tracts terminate, are particularly large and form the greater part of the protuberant thalami. There are also two end nuclei of some of the optic fibres which are supposed to represent the lateral geniculate bodies. On the other hand, the connection between the hypothalamus and cerebellum is usually very weak. The fasciculus longitudinalis posterior rises partly from the hypothalamus, but mainly from a large-celled nucleus in the floor of the mid-brain. The epiphysis is in most cases strongly developed, and in Lacertilia is in connection by its distal end with a median vestigial eye lodged in a foramen in the cranial roof. The infundibulum shows scarcely any signs of a saccus vas- culosus except in the swimming forms. The cerebellum, as in Amphibia, owing to the small size of the tracts that enter it, has no clearly defined inner fibrous layer. In the Reptiles there is an increase in the mimber of acoustic nuclei, corresponding to the development of a rudimentary cochlea (lagena). LACEETILIA. D. 127. The brain of a Monitor Lizard ( Varanus varius). In general form this is a typical example of the brain of a Reptile. The olfactory bulbs are long and narrow, and are united by short peduncles to the pear-shaped hemispheres. The hemispheres form the broadest part of the brain, and parts of them, representing the pyrif orm lobes, bulge down- ward behind the tuberculum olfactorium to form pseudo- temporal lobes. Posteriorly they are contiguous with the anterior face of the optic lobes and completely cover the thalamencephalon. In the dorsal mid-line, between the cerebrum aud optic lobes lies the club-shaped epiphysis, with a small vestigial eye in connection with its distal end. The optic lobes are well developed, and form a pair of rounded eminences separated from one another in the mid- line by a deep furrow. VOL.^II. I 114 PHYSIOLOGICAL SERIES. The cerebellum is of moderate dimensions and has the plate-like form usual among Reptiles. It is concave in front and arches forward slightly over the optic lobes. The medulla shows well the characteristic Reptilian flexure. Its fourth ventricle (rhomboid fossa) is considerably restricted. OPHIDIA. D. 128. A Ringed Snake {Tropidonotus naheres. The extraordinarily twisted form of the pyriform lobe is quite distinctive of this brain. Tliis is s^eii to advantjige on the left side, in which the neopallium has in great part been removed and the pyriform lobe left (fig. 40). Fig, 40 (Nat. size.) HlH PYR . L . The olfactory bulb slightly overlaps the tuberculum olfactorium posteriorly. The olfactory tubercles are very large, but are so placed in the floor of a deep depression, the prominent lips of which are formed by the pyriform lobes, that their greatness is not apparent. Behind this fossa the latter almost meet, so much are they bent towards the mesial plane (fig. 39). In the deep cleft between them the delicate optic nerves may be seen. Emerging between the posterior part of the pyriform lobes and the pons Varolii are the ribbon-like trigeminal nerves. It is a peculiarity of the Monotremata that the trigeminal nerves are inserted into the brain-stem wholly in front of the pons. Note the large size of the auditory nerve, which is placed immediately behind the point where the pontine fibres enter the cerebellum. The other cranial nerves call fot: no special comment. In spite of the great size of the pallium, the pyramidal tracts are so insignificant that they form no prominence on NERVOUS SYSTEM. — VEKTRBRATA. 149 the surface. The roots of the hypoglossal nerve, however, serve to indicate the lateral limit of each pyramid. There is a diffuse crossing of the fibres of the pyramids, instead of the compact decussations found in most mammals. The trapezoid body, which is such an obtrusive feature of most mammalian brains, is not recognisable as such by the naked eye in the Monotremes. The cerebellum is noteworthy for the small dimensions of its lateral parts, and from the fact that its structural plan cannot be certainly brought into harmony with that which is common to all the Meta- and Eutheria. It, how- ever, closely agrees with that of the Platypus. But there is a large sessile floccular lobe, in marked contrast to the pedunculated, encapsuled flocculus of the Platypus. In the left cerebral hemisphere the lateral ventricle has been opened so as to expose the hippocampus. The latter presents an appearance which is characteristic of the Monotremes. For, although the hippocampus also extends through the whole length of the lateral ventricle in the Marsupials, as it does here, it is only in the Monotremes that we find the largest and plumpest part of the hippo- campal arc occupying the dorsal and cephalic position. The caudo-ventral part of the hippocampal arc rapidly tapers to a point in Tachyglossus, and even to a more marked degree in Ornithorhynclms. 0. C. 1323*. Ziehen, Semen's Forschungsreise, Jena. Denkschr. Bd.vi. 1897, p. 4. D.192. The l^A cerebral hemisphere of a Spiny Anteater {Tachy- glossus [Echidna] aculeatus) : also a coronal section of another left hemisphere. A rough area in the centre of the mesial surface of the hemisphere indicates the place from which the optic thalamus was detached (fig. 41) . In front of this area the elliptical sections of two commissural bands are to be seen The lower or ventral commissure (comm.v.) is much the larger of the two and contains nervo-fibros corresponding to the anterior commissure of other mammalian brains. But, as the coronal section (fig. 42) [which passes through the two commissures] clearly shows, the ventral commissure 150 PHYSIOLOGICAL SERIES. has a much wider distribution than the anterior com- missure of most Eutheria, for it connects the whole of the two cerebral hemispheres, excepting the hippocampal formations only. Now in all Eutheria part of the neopal- lium is connected to the other hemisphere by means of the corpus callosum, so that the ventral commissure of the Spiny Anteater represents not only the anterior commissure, but also the corpus callosum of the Eutheria. Fig. 41. (Nat. size.) FASC.DENT COMM.D. OLF. BULB COMM. V 4-FASC.OENT. -A ■pYR.L. Fig. 42. (Nat. size.) FASC.DENT..__ CDAUVl. D> COMM. v..---- PYR. L.- CORP. ST. SYL.F. RHIN. F The dorsal or hippocampal commissure (comm.d.) is much smaller. It was erroneously believed by Flower (Phil. Trans. 1865) to represent the corpus callosum ; but as it is wholly derived from the hippocampal formation by means of the fornix, it cannot be strictly regarded as the representative of a commissure (the corpus callosum) which is derived from cortical areas (neopallium) other than the hippocampus (Elliot Smith, Proc. Linn. Soc. N. S. W. vol. ix. 1895, p. 635) *. • This view, which was originally stated by Owen in 1837, and conclu- sively demonstrated by modern methods by Symington (Journ. Anat & Phys. 1892), has recently been called in question by several writers, without a tittle of evidence to justify their irrational refusal to recognise a fact which is unquestionable and so easUy demonstrable. NEBVOUS SYSTEM. — VERTEBRATA. 151 Upon the upper surface of the dorsal commissure there is a narrow band of cortical substance, which is obviously the cephahc prolongation of the fascia dentata. A study of the mesial surface of the hemisphere shows this at a glance, and an examination o£ the coronal section confirms the opinion that the structure in question is really the fascia dentata. The caudal portion of this structure may be seen (behind the rough area on the corpus striatum) occupying the position in which we are accustomed to look for it in the Eutherian brain. It appears to be depressed below the level of the rest of the surface, because the neopalhum tends to bulge over the marginal hippocampal region. The clearly-defined hippocampal fissure separates the fascia dentata from the neopallium. But, unlike the arrangement found in the higher mammals, the fascia dentata (with the hippocampal fissure bounding it on its dorsal or peripheral side) extends far forward above the dorsal commissure. This explains the presence of the hippocampal formation in the pecuhar position in which it is seen in the coronal section. There (fig. 42) we see the fibres of the small dorsal commissure spreading out to form the ventricular covering (or alveus) of the hippocampus, from which they are wholly derived. By means of this section, it is easy to correlate the appearance of the ventricular surface of the hippocampus (seen in the last specimen, fig. 40) with the mesial distribution of the fascia dentata (which is merely a specialised marginal fringe of the hippocampal formation) in the hemisphere of this specimen. It is now also possible to understand how it is that the dorsal commissure is derived from the hippocampus. (Elliot Smith, Jouru. Anat. & Phys. vol. xxxii. 1897, p. 32.) The hippocampal fissure extends only a short distance beyond (i. e. in front of) the dorsal commissure, so that the fascia dentata (of which it forms the dorsal boundary) appears [in a spirit- preserved specimen] to blend with the neopallium above it, and also with the precommissural area below it. In a fresh brain the fascia dentata may, however, be readily distinguished by its colour, and may be traced forward into close proximity to the olfactory peduncle. PHYSIOLOGICAL SERIES. [In this specimen the olfactory bulb has been removed, and the irregular cut surface of its peduncle can be seen upon the ventral surftice of the anterior pole of the hemisphere.] At the concave margin of the postcommissural part of the fascia dentata there is a strand of white fibres — the fimbria or fornix. This consists of a group of fibres collected from or going to the hippocampus. In all Marsupials and placental mammals the fimbria projects as a prominent crest ; but in both Monotremes it consists merely of a slight thickening of the edge of the alveus, which does not project to form a ridge. Anteriorly its fibres appear in this specimen to pass bodily into the dorsal commissure, but many of them do not do so. A considerable proportion of the fibres of the fornix bend downward behind the ventral commissure as a compact bundle (the anterior pillar or column of the fornix), which enters the optic thalamus and proceeds toward the corpiTS mammillare : others again enter the precommissural area, and are known as the precommissural fibres (of Huxley). These fibres can be satisfactorily seen only in fresh specimens or in histological preparations (compare Journ. of Anat. & Phys. vol. xxxii. fig. 6, p. 36). In this specimen the fissures and sulci may be studied with advantage. The rhinal fissure is extraordinarily deep in the Mono- tremes, and especially in Tachyglossus, as the coronal section (fig. 42) shows. It pursues a very tortuous course on the lateral, ventral, and caudo-mesial surfaces of the hemisphere. Just before it leaves the lateral to reach the basal surface of the hemisphere, it gives off a short horizontal branch as deep as itself. This branch is probably produced by factors analogous to those which cause the so-called "Sylvian fissure " in other mammals ; it is, in other words, a kink produced by the downward growth of the neopallium behind it, and, as such, has a claim to be called the " Sylvian fissure" equal to that of, say, the Cat's brain. At the same time there is no reason for regarding it as a strict homologue of the similarly-named fissure of other mammals. The same term is used simply as a matter of con- venience in the same way that it is applied to the Edentate, NERVOUS SYSTEM. — VERTEBRATA. 153 Carnivore, Ungulate, and Primate brain respectively, in wliicli no exact correspondence exists. We know from the distribution of the claustrum that the exact cortical areas from which the lips of the Sylvian fissure are formed in diflPerent higher Orders [or even Suborders and Families — compare the Cynoidj Arctoid, and Pinniped Carnivores and the progressive modifications in their various families] are not strictly homologous in diflTerent mammals ; so that if we use the term " Sylvian for all these various types of fissure, we are also justified in using it for the fissure of the Spiny Anteater's brain, which is clearly caused by analo- gous factors of growth, without thereby implying any strict homology in the cortical areas which form its lips. It will avoid much confusion, however, if we call this sulcus (fig. 43, SYL.F.) " pseudosylvian." Fig. 43. (Nat. size.) The sulci of the neopallium of the Spiny Anteater vary very considerably in different individuals, and there is no clue to indicate whether any of them should be regarded as the representative of a sulcus of other mammalian brains. On the other hand, the arrangement of the sulci suggests that they might be due to purely mechanical factors operating in an uniformly growing pallium, the longi- tudinal expansion of which is restricted. The most constant of all the sulci are three distinguished as a, /3, and yfr in the diagrams (figs. 38 and 43). [The figures (38, 39, and 43) illustrating this account are drawn from the preceding specimen (D. 191) in order that both hemispheres might be represented. The description, however, applies more especially to this specimen (D. 192), PHYSIOLOGIOAL SERIES. in order that the arrangement of the sulci on the cranial surface may be compared with that of the mesial surface (fig. 41).] The sulcus a begins immediately behind the pseudo- sylvian, and pursues a course upward, i. e. mesially, to terminate just in front of the caudo-mesial angle of the dorsal surface. The sulcus y\r is the deepest and most constant of the radiating sulci on the mesial surface of the hemisphere. It appears to spring from the hippocampal fissure at a short distance behind the supracommissural exposed portion of the fascia deutata. In most brains it crosses the dorsal edge and joins the sulcus /3 on the dorsal surface. The latter pursues a course for a variable distance in front and parallel to the sulcus a. Its mode of termination is variable. In this specimen it bends forward opposite the mid-point of the sulcus a, and, after a short oblique course, ends in a bifid extremity. In the other specimen (D. 191) it behaves in a different manner (fig. 43, /3). In specimen I). 192 there is a short sulcus below ^, which may be regarded as a part of the same sulcus, as the two are commonly united as in specimen D. 191. On the dorsal surface o£ the hemisphere there are commonly two oblique or sagittal sulci (fig. 38, S and e), and behind them a short sulcus 7, parallel to « and ^. Behind there are two sulci, ? and ?/, and behind these again two others, o and /u,. The greater part of the hemisphere is thus divided into a series of slightly oblique transverse bands by the series of sulci, 7, A a, ^+1?, and o + ^l. The shallow sulcus tt on the mesial surface (fig. 41) is placed above and parallel to the anterior part of the hippocampal fissure *. It is very significant that the most constant and primitive sulci of the Meta- and Eutherian neopallium, such as the calcarine (splenial), orbital (presylvian), and suprasylvian sulci, are absent. This is one of the many manifestations of the great gap which separates the Monotremes from all other mammals. Presented hj Prof. G. Elliot Smith. Waldeyer (Review only), Merkel and Bonnet's Ergeb- * The indicating letter n has been omitted in the figure. NERVOUS SYSTEM. — VEETEBRATA. 155 nisse, Bd. viii. 1898, p. 372. (The more recent work by Bela Haller [Morph. Jahrb. 1900, p. 463] is quite mis- leading.) D. 193. The left cerebral hemisphere of a Spiny Anteater {Tachy- fflossus [Echidna] aculeatus) , dissected to show the hippo- campus in the lateral ventricle. In this specimen parts o£ the mesial wall have been torn asunder, and as a result the exact shape of the hippocampus can be seen to better advantage than in specimen D. 191. The latter specimen shows the same structures, however, in situ. D. 194. A cast of the cranial cavity of a Spiny Anteater ( Tachi/- glossus aculeatus). Gervais, Nouv. Arch. d. Mus., t. v. 1870, p. 247. D. 195. The optic thalami, mid-brain, cerebellum, and medulla oblongata of a Spiny Anteater [Tacky glossus [Echidna] aculeatus) . Fig. 44. (x2.) This specimen was prepared by the late Sir William (then Professor) Flower (see Proc. Zool. Soc. 1864, p. 18) to demonstrate the corpora quadrigemina, concerning the existence of the posterior pair of which some doubt had been raised by the writings of his predecessorj Sir Richard Owen. On the dorsal aspect (fig. 44) the small oval masses of the optic thalami will be observed in front, separated by 156 PHYSIOLOGICAL SERIES. the narrow mesial slit-like third ventricle. At its caudal extremity a blunt rounded sac is found representing the pineal body, and in front of this the ganglion habenulse and tjenia thalami are found on each side of the ventricle, as in all other vertebrate brains. Perhaps the most significant feature of this specimen is the absence of any protuberance corresponding to the mesial geniculate body. In this respect the Monotreme brain differs most markedly from that of all other mammals. The absence of any markedly projecting lateral geniculate body is not so pecuhar, not only because this body is not prominent among the lowlier mammals, but also because the visual apparatus, of which it forms an important part, is poorly developed in the Monotremes. The quadrigeminal bodies are comparatively small and flat as comparedwith those of other mammals. The pons Varolii is prolonged into a forwardly-projecting process or rostrum in the mesial plane, probably because the nuclei pontis are scattered throughout a much greater antero-posterior extent than the narrow lateral parts of the pons occupy. This peculiar rostrum is distinctive of the Monotremes, since it is also found in the Platypus. Im- mediately in front of the rostrum note the interpeduncular body, one of the oldest parts of the brain in the phylogenetic sense. The rounded knob formed by the corpora mam- millaria, the oculo-motor nerves, and the delicate optic tracts conform to the usual mammalian type. In comparison with the corresponding organ in other mammals, the cerebellum in the Monotremes presents features so peculiar that no exact comparisons with that of other mammals can be instituted with any degree of certainty. The fissura prima (praeclivahs of Human Anatomy) is apparently placed very far back, so that the greater part of the cerebellum, including the whole of the anterior and the greater part of the dorsal surface, corre- sponds to the anterior lobe of other mammals (the combined lobus centralis and lobus culminis of Human Anatomy). Thus the whole of the postclival region, which in the higher mammals becomes so greatly expanded that it forms the biilk of the organ, becomes relegated to the caudo-ventral region NERVOUS SYSTEM. — VERTEBRATA. 157 o£ the cerebellum and is a narrow insignificant strip, which is expanded laterally only to a very slight degree. The region of the nodulus agrees with that of other mammals. The floccular lobe is sessile in Tachyglossus, but projects for a considerable distance in Ornithorhynchus . It is a simply foliated appendage, and is not divisible into flocculus and paraflocculus ; nor can a ventral and dorsal segment be recognised as in other mammals, although the radiating feather-like arrangement of the folia in Tachyglossus is a simplified form of the two-layered type of paraflocculus. The cerebellum differs in a most marked raanner from that of other mammals, and seems to be a highly specialised modification of the primitive mammalian type. Its most significant feature is the relatively small size of its lateral parts. Seeing that most of its exposed part probably represents the anterior lobe of the mammalian cerebellum, in which there is no clear line of demarcation between vermis and lateral hemispheres, such distinctions are also lacking in the Monotreme. 0. C. 1323**. Ziehen, Semon^'s Forschungsreise, Jena. Denkschr. 1897, p. 23. D. 196. The cranial cast of a so-called " Proechidna" {Proechidna hniijni). The brain is distinctly larger than it is in T. aculeatus ; the olfactory bulbs project much further beyond the hemi- spheres ; the hemispheres are proportionately much longer than in the other species and are extremely large and richly convoluted for so lowly a mammal. Gervais, Nouv. Arch. Mus., t. v. 1869, pi. xiv. OitDEK MAESUPIALIA. Suborder polyprotodoktia. ramily Basyubjdje. D. 197. The brain of a Tasmanian Devil {Sarcopliilus [^Dasyurus] ursinus) ( $ ), in which the left cerebral hemisphere has been separated from the rest of the brain. PHYSIOLOGICAL SERIES. This is one of the simplest and most generalised types of the mammalian brain, and presents a marked contrast to the specialised Monotreme organ. Its most obtrusive feature is the relatively enormous size of the olfactory bulbs, which are attached by short thick peduncles to the front of the cerebral hemispheres. In the great majority of mammals the olfactory apparatus is largely developed ; and in the case of a terrestrial, offal- eating animal, like Sarcophilus, the importance of the sense of smell becomes enormously enhanced and it becomes the dominant sense. This finds expression (as in Perameles, ride fig. 52) in the huge development of the olfactory bulb, in the large elliptical olfactory tubercle on the base of the brain, in a pyriform lobe which forms a large part of the ventral surface and almost half of the lateral aspect of the Fig. 45. (Nat. size.) X SULC.ORB. / OLF.TR. olf! TUBER."* hemisphere, and in a large hippocampal formation which forms a considerable part of the mesial wall. This brain shows very clearly the definite connections which the olfactory peduncle establishes with both the lateral and mesial walls of the cerebral hemisphere. Upon the lateral aspect (fig. 45) the peduncle is directly continued into the pyriform lobe, and a layer of medullary fibres upon the latter becomes collected into a definite bundle -the olfactory tract or so-called " external olfactory root "—which proceeds backwards in the shallow groove between the pyriform lobe and the olfactory tubercle, distributing fibres over the surfaces of both. The tract finally ends in a little nodule behind the olfactory tubercle (fig. 45, *) , which may be called the tubercle of the olfactory tract [Retzius calls it the " gyrus intermedins "]. NERVOUS SYSTEM. — VERTEBRATA. 159 A well-defined rhinal fissure begins anteriorly in the cleft between the olfactory bnlb and the apex of the hpmis])here, and separates the pyriform lobe from the neo- pallium. Upon the mesial surface (fig. 46) the olfactory bulb may be distinctly seen to be connected by a short cylindrical peduncle to the precommissural area of the mesial wall. The tuberculum olfactorium is seen immediately below the latter. In the caudal region of the mesial wall the fascia dentata and fimbria are seen presenting features such as we find in most mammals. The prominent, broad fimbria at once distinguishes this hippocampal formation from that of the Monotremes. Fig. 46. (Nat. size.) HJP. F. SULC.CALC. DLF, tuber:' 'zOMM.V. This fimbria is seen to pursue a regular arcuate course upward and forward to reach a point immediately above the large ventral (modified anterior) commissure ; and many of its fibres then cross the middle line in close relation to the upper extremity of the lamina terminalis, so as to form a smaller dorsal commissure, which is thus derived by means of the fornix (fimbria) from the hippo- campus. Histological examination shows that the fibres of this dorsal commissure are not grouped irregularly to form a round bundle, as in the Monotremes, but are compactly arranged in a crescentic form. In some Marsupials this dorsal commissure becomes more acutely bent so as to be distinctly bilaminar. Some of the fibres of the fimbria do not enter the dorsal commissure and are divided into two groups, a scattered anterior group of pre- commissural fibres and a posterior group — the so-called anterior pillar of the fornix — which proceeds behind the ventral commissure and passes through the optic thalamus toward the corpora mammillaria. PHYSIOLOGICAL SERIES. The fascia, dentata (like the bippocampal fissure which marks its poriplieral boundary) proceeds upward and forward alongside the fimbria as far as the dorsal commissure; and then it passes forward above the dorsal commissure and appears to lose itself in the precommissural area immediately above the attachment of the olfactory peduncle. In a fresh brain (or by means of histological examination) the fascia dentata may be traced forward practically into continuity with the olfactory peduncle (Trans. Linn. Soc, Zool. ser. 2, vol. vii. 1897, pi. 15. fig. 8). The hippocampal fissure accompanies the fascia dentata in the greater part of its course, but stops just as it approaches the neighbour- hood of the olfactory peduncle. The mesial surface of the olfactory peduncle passes backward into direct continuity with the precommissural area, which is separated above by the fascia dentata from the neopallium. This precommissural ai*ea is continuous below with the tuberculum olfactorinm, and is bounded posteriorly by the lamina terminalis containing the dorsal and ventral commissures. The retention in an undisturbed state of the cephalic portions of this hippocampal formation is the most interesting feature in the brain of the Marsupial. In this it agrees with the Monotreme, but is the more instructive because the caudal parts of the hippocampus in the Marsupial have assumed the configuration which is met with in other mammals. The cephalic parts of the hippocampal formation are retained in the Marsupial because the dorsal commissure is derived from the hippocampus, and the great non-hippo- campal commissure (corpus callosum) has not yet made its appearance to disturb the integrity of the hippocampal arc. It is the absence of the corpus callosum and the retention of the supracommissural and precommissural parts of the hippocampus undisturbed that renders the cerebral hemi- sphere in the Monotremata and Marsupialia so instructive to the student of the higher mammalian brains. For the corpus callosum consists of a series of fibres at first intermingled with those of the dorsal or hippocampal commissure, but distinguished from them by the fact that they come from a cortical area (the neopallium) other than NERVOUS SYSTEM. — VERTEBRATA. 161 the hippocampus and do not form part of the fornix. But as this series of neopallial fibres increases in number in the Eutherian brain, the corpus callosum rapidly extends and assumes the large dimensions which we usually associate with this body. As it does so it naturally stretches a portion of the great hippocampus (of which the fascia dentata forms the only part visible upon the surface), and the hippocampus atrophies in the region of stretching. Thus in all mammals possessing a corpus callosum, the hippocampus persists in an unchanged state only so far forward (or so far up) as the splenium of the corpus callosum, but its anterior part is represented by vestiges upon the upper surface of the corpus callosum and along a line joining the anterior extremity of the latter to the olfactory peduncle. In man these vestiges together with some longitudinal fibres in connection with them are generally known as the longitudinal strise of Lancisius. (For a fuller elucidation of these peculiarities see Journ. Anat. & Phys. vol. xxxii. 1898, p. 30.) The precommissural area is also of interest in the Marsupial, in view of the fact that in most other mammals the upper part of the corresponding region becomes stretched by the growing corpus callosum to form a folium of the septum lucidum in each hemisphere. Upon the postero-superior region of the mesial wall of the hemisphere, there is a short arcuate sulcus running parallel to the hippocampal fissure. The corresponding sulcus in the Ungulata was named the '^Jlssura splenialis " by Krueg, from its relationship to the splenium of the corpus callosum. There can be little doubt that this sulcus represents the anterior calcarine sulcus [z. e. the true calcarine fissure, the stem of the Y-shaped complex] in the human brain, and hence we may call it " calcarine " in Sarcophilus (Elliot Smith, Proc. Anat. Society, 1899) *. * For the demonstration of this homology compare the conditions found in Manis, Choloipus, Daubentonia and the other Primates. The most diverse views are put forward by various writers as to the possibility of homologising the sulci of one brain with those of another. Some writers attempt to institute comparisons upon a purely topographical basis between the cerebral sulci of brains of even different Orders of VOL. II. M 162 PHYSIOLOGICAL ■ SERIES. In the smaller Dasyuridai this sulcus is not present. The cranial surface of the hemisphere is not quite smooth. The rhiual fissure separates the pyriform lobe from the Fig. 47. (Nat. size.) neopallium, and in addition the latter is also marked by several shallow furrows (figs. 45 and 47). Of these the mammals ; whereas others go to the opposite extreme and deny in toto the possibility of homologising the sulci fomid in one Order of mammals with those of another. There can be little doubt that the fundamental constituents of many of the sulci found in the Metatheria and Eutheria are morphologicaUy stable elements which cau be certainly homologised in many different Orders. The exact homology of the hippocampal and rhinal fissures in all mammals is beyond question, because the pecuUar histological features of the lips of these fissures enable us to certainly identify them. The developmental history and the behaviour of the fundamental constituents of the calcarine sulcus of Primates and the upper part of the vertical ramus of the sulcus commonly called " splenial " in other mammals indicate their identity. In the same manner we can recognise the suprasylvian, lateral, coronal, and orbital (presylvian) sulci in the most diverse Orders of mammals. Most of these names were originally applied to the Carnivora {vide infra). By "fundamental constituent " I mean the stable basis of a sulcus, which seems to be produced (even when the mechanical conditions must be vastly different) in various Orders of mammals in response to some factors other than the' mere general expansion of the neopallium. The extending cortex may be accommodated in the neighbourhood of such a sulcus by tlie prolongation of the latter : or, agaii-, the furrow in question may become confluent with various other sulci in different mammals. Thus the calcarine sulcus (sensu stricto, i. e. the short post-splenial furrow, which indents the wall of the NERVOUS SYSTEM. — VBRTEBRATA. 163 deepest and most constant is a short oblique furrow situated just above the mid-point of the anterior rhinal sulcus (i. e., the anterior horizontal part of the rhinal). It represents the presylvian sulcus, which is one of the most constant features of the mammalian neopallium. There are many reasons for regarding this presylvian sulcus as the earliest form of the sulcus known in Human Anatomy by the name "orbital."^ [Compare the account of the Prosimian brain.] Behind the upper extremity of this sulcus there is a shallow transverse depression (figs. 45 & 47, x), which is of interest because the brain of Thylacimis, the large relative of SarcopJdkis, exhibits a deep sulcus in the corresponding position. Above and parallel to the posterior rhinal fissure there is a short horizontal sulcus, and in front of it a small triradiate sulcus (t). These clearly represent the great sulcus, which I have distinguished as " horizontal " in the venti-icle and thus produces the calcar avis) is undoubtedly a definite morphological feature, which is the common property of the Meta- and Eutheria. Yet in the Cai-nivora, Ungulata, and many other mammals its ventral end may he prolonged almost or quite as far as the rhinal fissure, merely because the expanding cortex in this region is most readily accommo- dated by the extension of this already-existing sulcus. In the Carnivora and Ungulata the upper end of the calcarine sulcus becomes confluent with the intercalary sulcus, forming the so-called "splenial." In the Primates the lower end of the calcarine sulcus does not become prolonged and the upper (posterior) end joins, not the intercalary, but the postcalcarine sulcus. Now, in such a catalogue as this, it is quite impossible to explain on every occasion whether it is the " calcarine," or the " prolonged calcarine," or a " calcarine complex " to which we refer, without endless confusing periphrases, which would make the accounts hopelessly involved. The same kind of misunderstanding might arise also in the case of the suprasylvian, lateral, or orbital sulcus. The reader must therefore bear in mind that the same names are employed in different Orders in order to indicateas concisely as possible where to look for the homologous sulci, rather than to suggest the identity of the whole of any sulcits called by any given name. It is also impossible to discuss in a catalogue of limited dimensions all the reasons which have led to the adoption of the views set forth in the brief accounts of the various specimens. The student who is not acquainted with the nomenclature used for the sulci is referred to the figures of the brain in the Carnivora (infra). M 2 PHYSIOLOGICAL SERIES. Thylacine (fig. 50). It is not possible to suggest any homology between this and a named sulcus of any other mammalian brain. The neopallium in the Tasraanian Devil thus exhibits features of interest as a connecting Hnk between the smooth hemispheres of the smaller Dasyurids and the deeply fissured hemispheres of the Thylacine, the sulcal pattern of which it so clearly foreshadows. The base of the brain (compare with Perameles, fig. 52) presents features which differ in a very marked manner from those of the Monotreme brain, and closely agree with the characters of the vast majority of other mammals. Thus the pons presents the appearance of an almost uniform transverse band and lacks the peculiar rostrum of the Monotreme ; moreover, the majority of its fibres pass in front of the trigeminal nerve ; the pyramidal tracts appear as prominent bands which decussate in a more or less compact mass, and not as a diffuse crossing, as in the Monotremes : the trapezoid bodies, which are not recognisable as such to the naked eye in the Platypus and the Spiny Anteater, are now very prominent and well- defined features. Each half of the trapezoid body consists of a large strand of fibres which springs from the acoustic tubercle (where the nerve-fibres from the cochlea end), and, after pursuing a transverse course on the caudal side of the pons, dips into the medulla and passes chiefly into the lateral fillet of the opposite side. It constitutes the chief cerebral path for auditory impulses. The pituitary body has been torn away with the iufun- dibulum, so that the mesial slit-Hke third ventricle has been opened up between the large optic chiasma and the distinctly paired corpora mammillaria. In the depression behind the latter note the large interpeduncular body in contact with the pons. The cerebellum conforms to a simple type such as we find in the Insectivora, Rodentia, Chiroptera, and Dasy- podidffi (Edentata). Projecting upon each side there is a large irregular mass of folia resting upon the lateral aspect of the pons and medulla oblongata, and separated from the NBKVOUS SYSTEM. — VBETEBRATA. 165 rest of the cerebellum by a deep fissure. This is the floccular lobe. In man the representative of this mass becomes reduced to very insignificant proportions and forms the flocculus. In this brain, however, the floccular lobe is almost, if not quite, equal in size to the whole of the rest of the so-called lateral lobe. Two shallow sagittal grooves separate the upper surface of the cerebellum into three projecting ridges, each of which is subdivided by a small series of transverse furrows. In each of these grooves a triangular area of medullary matter is exposed. The area seen in this specimen between the floccular lobes corresponds to that region of the human cerebellum which lies behind and below the preclival fissure and in front of the uvula. Part of the uvula in this specimen may be seen as a little tongue-like process extending backward and forming an operculum over the apex of the fourth ventricle. The most significant feature of this organ to the human anatomist is the extreme diminution of the lateral hemispheres; but when the intimate association existing between the cere- bellar hemisphere and the opposite cerebral hemisphere is remembered, it is not surprising to find these parts of the cerebellum so poorly developed in a brain in which the pallium as a whole, and especially the neopallium, is so diminutive. The anterior lobe, which is relatively so large in the Monotremes, is completely hidden in this brain by an overhanging hood formed by the region lying behind the fissura prima (vel praeclivalis). 0. C. 1323 B b. R. Owen, Todd's Cyclopaedia, 1847, vol. iii. p. 291. D. 198. The brain of a Tasmanian Devil (SarcopMlus [JDasyurus] ur sinus) . This specimen shows the real proportions of the huge olfactory bulbs. The hemispheres have been drawn apart so that a much greater part of the corpora quadrigemina is exposed than when the parts are in their natural position. [Compare the casts D. 199 and fig. 47.] This specimen is represented in Owen's 'Anatomy of Vertebrates,' vol. iii. p. 104. 0. C. 1323 of. 166 PHYSIOLOGICAL SERIES. D. 199. Cast of the cranial cavity of a Tasmanian Devil {Sarco- pluLus \JJasyurus\ ursinus). [In duplicate.] This shows better than the actual spechnen (which is liable to distortion) the large proportions of the olfactory bulbs and the relations of the cerebellum (the chief divisions of which are clearly seen) to the cerebral hemispheres. Note the orbital sulcus on the hemisphere (fig. 45) . P. Gervais, Nouv. Archiv. Mus., t. v. 1869, PI. xiv. fig. 8. D. 200. A young Australian " Native Cat " {Dasyurus viver- rinus), with the brain and spinal cord exposed in situ. Parts of the hemispheres have been removed so as to expose the hippocampi from above. 0. C. 1323 C b. D. 201. The right half of the brain of an Australian " Native Cat " (J}asyurus viverrinus), separated by a mesial sagittal section. Two white bristles have been inserted into the hippo- campal fissure just above the prominent fascia dentata which rests upon the dorsal commissure. A black bristle has been inserted just below the ventral (anterior) commis- sure and another in the centre of the large " soft " or " middle commissure " (so-called). The cavity of the third ventricle in which the latter is placed may be clearly seen in this specimen. Its communication with the lateral ventricle, viz., the foramen of Monro, may be distinctly seen in the ffroove between the dorsal and soft commissures. Note the large size of the aqueduct of Sylvius, which opens from the posterior extremity of the third ventricle into the mid-brain. The roominess of this canal is very suggestive when it is recalled that in most submammaliau forms a ventricle exists in this situation and extends into the " optic lobes." Note further the simplicity of the cerebellum. Its deepest fissure— the fissura prima — opens on the anterior surface near the apex of the organ : it is the homologue of the preclival fissure of Human Anatomy. All of these features (excepting the arrangement of the hippocampus and the commissures) are connnon to other lowly mammalian brains, such as those of the Insectivora. 0. C. 1323 c. NERVOUS SYSTEM. — VERTEBRATA. 167 D. 202. The right cerebral hemisphere, the caudal part of the left cerebral hemisphere, and the brain-stem and cerebelhira of a Tasmanian "Wolf" [Thylacinus cynocephalus). The mesial aspect of the hemisphere (fig. 48) presents . the typical arrangement of the cerebral commissures and hippocampiis ; and, as such, this identical specimen was figured by the late Sir William Flower (Phil. Trans. 1865). Fig. 48. (xf.) He, however, erroneously regarded the dorsal commissure as a true corpus callosum. There is a well-developed calcarine sulcus beginning just above thb caudal extremity of the rhinal fissure. It is prolonged upward and forward after the manner of the splenial complex in many orders. An oblique section has been made through the left hemi- sphere (fig. 49) (in the plane indicated in fig. 48) in the Fig. 49. (x§.) region of the deepest part of the calcarine sulcus. The latter is thus shown to be "complete" or "total"; in other words it gives rise to a bulging — the calcar avis or so-called hippocampus minor — in the ventricle immediately to the peripheral side of the true hippocampus. There is a deep and sharply-defined rhinal fissure, acutely bent . at the junction of its anterior and posterior parts PHYSIOLOGICAL SERIES. (fig. 50). A deep and extensive orbital (presylvian) sulcus springs from the rhinal a short distance in front of the angle and proceeds transversely across the hemisphere as two conjoined arcs. The upper arc, the convexity of Fig. 50. (xf.) Qtf.aULB which looks backwai'd, was probably a distinct sulcus originally. Here it has fused with the orbital sulcus (figs. 50 and 51). It extends on to the mesial wall of the hemi- sphere (fig. 48), immediately behind a short upturned Fig. 51. (x§.) sulcus prolonged from the cephalic extremity of the hippo- cam pal fissure. A shor^ kink-like depression extends upward from the angle of the rhinal fissure for a short distance, and may NERVOUS SYSTEM. — VERTEBRATA. 169 be regarded as analogous to the "Sylvian fissure" of Carnivores *. A deep sulcus (y) begins near the posterior margin of the hemisphere and pursues a course parallel to the posterior rhinal almost as far forward as the " Sylvian fissure." Its anterior extremity is joined by a shallow oblique sulcus to a second deep furrow (x) which pursues the same direction as the posterior sulcus but on a slightly higher level. The whole complex forms a great sulcus crossing the hemisphere obliquely as far as the dorso-mesial edge, where it almost reaches the upper extremity of the prolongation of the calcarine sulcus (fig. 48) . The determination of the homo- logies o£ these furrows is fraught with great difficulty ; but it will be found, I believe, that the sulcus Y represents the suprasylvian and the furrow x the coronal sulci of other mammals. In the right hemisphere of a Thylacine described by Beddard the sulci x and Y overlap but do not join. In the left hemisphere of his specimen the condition described in this hemisphere is found. In front of the presylvian there is a short separate hori- zontal sulcus analogous to that called " prorean " in the Carnivora. On the left hemisphere it joins the presylvian. There is a shallow olfactory sulcus (i. e. the depression in the neopallium which lodges the olfactory bulb and peduncle.) There are also a few ill-defined punctate depressions below and above the x-Hy complex sulcus. The plan of the sulci is a more complete elaboration of that faintly foreshadowed in the Tasmanian Devil. It has undoubtedly considerably diverged from the plan found in most placental mammals, though not to such a marked extent as that of the Monotremes or even of the Diprotodont Marsupials. The optic tract may be seen spreading out on the lateral tubercle of the optic thalamus. Behind the latter note the * But this is a feature vastly different from the true Sylvian fissure of the Primates (vide infra). In the latter part of this work I have therefore dis- carded the erroneous name " Sylvian " and called it " pseudosylvian." The earlier part was already in print before I fully appreciated the utterly mis- leading effects of calling this furrow " Sylvian." 170 PHYSIOLOGICAL SERIES. large mesial (posterior) geniculate body and the great corpora qnadrigemina of which the anterior pair are especially prominent. The cerebellum conforms to the same plan as that of Sarcojyhilus. But the mesial and lateral parts of the region behind the primary fissure are unusually prominent. They are separated the one from the other by exceedingly deep broad furrows in which large medullary areas are exposed. The mesial "vermis" is twisted toward the right and the lateral areas are expanded in a feather- like pattern, such as is common in Carnivora, Edentata, and other Mammalian Orders. F. E. Beddard, Proc. Zool. Soc. 1891, pp. 140-145. D. 203. A cast of the cranial cavity of a Tasmanian Wolf ( Thylacinus cynocephalus) . This shows that the olfactory bulbs are laterally com- pressed and of large size ; they are borne on long peduncles so that they are placed almost wholly in front of the hemispheres. The peculiar shape of the cerebral hemispheres is clearly demonstrated^ and the relatively small size of the pointed apices which constitute the presylvian part of the hemi- spheres is shown. The positions of the sulci described in the actual brain are clearly indicated. The peculiar configuration of the cerebellum is also shown in a very striking manner. Gervais, Nouv. Arch. Mus., t. v. 1869, p. 229. Family PebamelidjE. D. 204. The brain of a Rabbit- Bandicoot {Thalacomys lagolis). [This specimen lacks the greater part of its olfactory bulbs and the projecting portions of the cerebellum.] The general features of this brain are like those of the brain of Dasi/urus, but the cerebral hemispheres are more distinctly conical. 0- C. 1323 C h. D. 205. The brain of a Bandicoot (probably P^rameles nasuta). This specimen was labelled "Dasyurus " in the old Cata- logue; but the pointed cerebral hemispheres, the pronounced lateral " spreading " of the caudal parts of the pyriform lobes, NERVOUS SYSTEM. — VERTEBRATA. 171 the simplicity of the cerebellum, and its markedly-projectiug, ])edunculated floccular lobes clearly show that it is the brain of Perameles. In fact, it exhibits the characteristic features of the genus in a much more distinctive manner than the specimen (D. 206) labelled " Perameles." In both speci- mens the large olfactory bulbs are damaged so that their great size is not properly shown. The brain of Perameles is even more generalised and simple than that of Dast/urus. It also closely resembles the brain of that most generalised of all Eutherian brains — the Hedgehog's — in all points except the arrangement of the commissures: for Erinaceus, Wke all Eutheria, possesses a true corpus callosum. Fig-. 62. (Nat. size.) The rhinal fissure is shallower and shorter than it is in SarcopJdlus : there is only a faint indication of the orbital (presylvian) sulcus, which closely resembles that of Erina- ceus ; the cerebellum is much simpler, and there are no exposed medullary areas between the mesial and lateral portions of the organ. The accompanying drawing (fig. 52) represents the characteristic features of the base of the brain in a fresh specimen. 0. C. 1323 c d. Gervais, Nouv. Arch. Mus., t. v. 1869, p. 242. [The reader is warned that Gervais' figure 12 on Plate xiii. obviously represents tlus brain of some small Macro- pod, and not a Perameles as it is labelled.] 172 PHYSIOLOGICAL SERIES. D. 206. The brain of a Bandicoot (Perameles sp.). The prominent floccular lobes (compare fig. 52) have been removed from this specimen. 0. C. 1323 ci, Family DidelphyidjE. D. 207. The brain of a Virginian Opossum {Didelphys marsu- pialis). This closely resembles the brain of Perameles and the Dasyuridce. Note the well-defined rhinal fissure which does not extend the whole length of the hemisphere, so that posteriorly the pyriform lobe and the neopallium become freely continuous. Note the shallow orbital (presylvian) sulcus, especially on the right hemisphere. The hemispheres have been separated in order to expose the dorsal (hippocampal) commissure placed in front of the third ventricle. The cerebellum is simple like that of Perameles. 0. 0. 1323 b. Herrick, Journ. Comp. Neurol, vol. ii. 1892, p. 1. D. 208. The brain of an Opossum (Didelphys) , with the arachnoid and pia mater in situ. This shows the true proportions of the olfactory bulbs and also how much of the corpora quadrigemina is uncovered by the cerebellum and cerebral hemispheres. 0. C. 1323 b a. Owen, Todd's Cyclopaedia, 1847, vol. iii. p. 292. Suborder Diprotodontia. Family MacropodidjE. D. 209. A series o£ five coronal sections of the cerebral hemi- spheres of a Bennett's Wallaby {Macropus rujicollis). These specimens serve to demonstrate a peculiar bundle of fibres (seen in the second section), the presence of which is peculiarly distinctive of the Diprotodont Marsupials. The uppermost section passes in front of the cerebral commissures and shows the relations of the precommissural NERVOUS SYSTEM. — VERTEBRATA. 173 part of the hippocampus to the neopallium above it and to the precommissural area below it. (These features are perhaps seen to better advantage on the back of the second slice.) (Fig. 53.) Fig. 53. (Xli) HIP. F. ^NEOPAL. 'OLF .TUBER. The second section (fig. 54) passes through the two cerebral commissures. The dorsal commissure is seen passing into the alveus of the hippocampus on each side. From this section it is possible to appreciate how the pallial operculum descends on the mesial side of the hippocampus toward the dorsal commissure, so as to shut out the fascia Fig. 54. ixlh) FAaC . DENT. COMM.V. COMM.D. dentata in a view of the mesial wall (compare the specimens of the Black-faced Kangaroo) . The ventral commissure is seen (in the second section) to split into two bundles in the corpus striatum. The ventral bundle, which includes about half the fibres of the commissure, passes transversely through the corpus striatum, and joins the external capsule. This is the manner in PHYSIOLOGICAL SERIES. which the whole of the neopallial fibres of the ventral commissure behave in the Monotremata (fig. 42), the Poly- protodont Marsupialia, and the Eutheria. But in all the Diprotodont Marsupials the dorsal half of the ventral commissure bends upwards in the corpus striatum, as it does in this section, and ultimately i-eaches the neopallium by the same route as that pursued by the internal capsule. This dorsal bundle I have called the "■ fasciculus aherrans." It was first represented in a figure by Flower (Phil. Trans. 1865), and first described by Symington (Journ. of Anat. & Phys. 1892) in Macropus. 1 have recently examined the brain in every genus of the Marsupialia (excepting Caeno- lestes), and found this "aberrant bundle to be invariably present in the Diprotodontia, but never in the Polypro- todontia, nor in other mammals. [This fact is here recorded for the first time.] The third section passes through the hemispheres a short distance behind the commissures, and the " splenium " of the hippocampal commissure is still seen in the depths of the slice above the slit-like third ventricle, which separates the optic thalami. This section passes through the optic chiasma. The fourth section has been cut still further back. It exhibits the fimbria on the hippocampal formation, and it is easy to understand b}' comparison with the third section how the fibres of the fimbria reach the dorsal commissure. O.C. 1323 a/. Symington, Jom-n. of Anat. & Phys., vol. xxvii. 1892, p. 69. 210. The left cerebral hemisphere of a Yellow-footed Rock- Wallaby {Petrogale xanthopus) , from which the lateral wall of the ventricle has been removed in order to expose the hippocampus (fig. 55} . The disposition of the hippocampus is the most character- istic feature of the brain in Marsupials, in all of which, both Poly- and Diprotodont, it presents a constant arrange- ment such as this specimen exhibits. Instead of being restricted to the descending limb and posterior part of the body of the lateral ventricle, as is the case in most NEEVOUS SYSTEM. — VERTEBRATA. 175 mammals, the hippocampus extends forward as a large arcuate bulging upon the mesial wall of the ventricle ; this proceeds above the cerebral commissures, and reaches a point near the cephalic extremity of the hemisphere. [Similar dissections have been made in brains of Erin- aceus {vide infi'a, D. 230) and Lepus {vide infra, D. 264) in order to demonstrate the difference between the Meta- and Eutheria in regard to this feature.] The anterior extremity of this great hippocampal arc is narrower than the more caudal part, and tapers to a rounded extremity. The inferior or caudal extremity is large and plump, and does not taper. In the Monotremes, which are the only other mammals possessing this hippo- campal arc in its undisturbed simplicity, its caudal portion Fig. 56. (Nat. size.) HIP. / is relatively small, and tapers to a point. In regard to these features, the Marsupial approaches much more nearly to the Eutherian plan than does the Monotreme. Upon close examination of the ventricular surface of the hippocampus a series of oblique fibres {alveus) may be seen proceeding from the hippocampus to form a fringe-like band at its concave margin. This is the fimbria or fornix, and is here seen in its most simple form. Elliot Smith, Journal of Anat. & Phys., vol. xxxii. 1897, p. 30. D. 311. The two cerebral hemispheres and the left half of the brain-stem and cerebellum of a Black-faced Kangaroo {Macropvs giganteus, var. melanops). Above the large elliptical ventral commissure, note the elongated, horizontally -placed, U-shaped dorsal (hippo- campal) commissure, the shape of which is characteristic of 176 PHYSIOLOGICAL 8EEIBS. the Macropodidaj. There is a typically complete hippo- campal arc of the usual Marsupial type, but its dorsal part is hidden by a great pallial operculum which descends as far as the dorsal commissure, so as to produce a spurious resemblance to the Eutherian condition. Such a neopallial operculum is found in all large Marsujuals, such, for in- stance, as the Thylacine. In the right hemisphere this pallial operculum has been removed by dissection (fig. 56), and the fascia dentata is thus seen to extend far forward above and beyond the dorsal commissure, just as it does in the Tasmanian Devil (D. 197) and in all Marsupials. The arrangement of the hippocampus in the ventricle may Fig. 56. (Nat. size.) COMM . D . FASC DENT. thus be correlated with the distribution of its specialised fringe (fascia dentata) in the mesial wall of the hemisphere. Above the upturned caudal extremity of the rhinal fissure a deep calcarine sulcus is found : it is prolonged ' obliquely upward and forward for a short distance so as to converge with an anterior oblique sulcus toward the dorsal edge of the hemisphere. This anterior oblique sulcus is apparently analogous to the genual sulcus of other mani- malian orders. Immediately in front of the genual sulcus and the anterior extremity of the hippocampal fissure there is a short rostral sulcus extending obliquely upward and slightly forward. On the right side it bifurcates and becomes Y-shaped. There is a deep and typically- bent rhinal fissure. From the neighbourhood of the angle of this fissure on the left hemisphere three sulci diverge widely in the neopallium. NERVOUS SYSTEM. — VERTEBRATA. 17T The interpretation of these raises a question of great difficulty. There can be little doubt that the most anterior represents the orbital or presylvian sulcus of other mam- mals*. It does not actually open into the rhinal fissure, but begins near it, and proceeds obliquely upward and forward. In this course it is joined by the anterior ex- tremity of a great inverted V-shaped sulcus, which may possibly represent the suprasylvian sulcus. But upon this question it is impossible to express a decided opinion at present f. The other two sulci which diverge from the angle of the rhinal fissure are probably to be regarded as essentially " Sylvian " (in the sense in which this term is applied, say, in speaking of the Cat's brain) . The more posterior, which we may distinguish as sulcus B, freely communicates with the rhinal fissure and with the sulcus tentatively called suprasylvian in such a manner that the presylvian and suprasylvian sulci, the sulcus B, and a short basal piece of rhinal fissure form a pentagonal pattern. The deep ver- tical sulcus which springs from the rhinal fissure between the lower ends of the presylvian sulcus and sulcus B may be distinguished as A. It ascends almost as far as the angle of the so-called " suprasylvian " sulcus. The sulcus which it is customary to call " Sylvian fissure " in mammals other than the Primates is a feature of little morphological stability, and is to be regarded as essentially of the nature of a kink produced by the flexure of the hemisphere. Or perhaps it would be more accurate to speak of it as being developed in response to the stress produced in this region of the neopallium by the ventral extension of its ventro-caudal region. In the Kangaroo this stress seems to be relieved by the two sulci A and B * Not the orbital pure and simple, but the orbital joiued to a second more dorsal (mesial) sulcus, the direction and situation of which is probably determined by the bias given to the expanding cortex by the presence of the orbital sulcus. Compare the left hemisphere of specimen D. 216. t Close examination shows that the anterior limb of the V — which is the smaller and more unstable element and may represent the coronal sulcus — is not joined to the caudal limb, which is the supposed homologue of the suprasylvian. VOL. U. IT PHYSIOLOGICAL SERIES. instead of the customary single sulcus, which is the so- called " Sylvian fissure." On the right heinisphere of this brain a third sulcus, which may be distinguished as C, shares the representation of the pseudosylvian furrow. The sulcus C is divided into two parts, but neither of these, nor the sulcus B joins the so-called suprasylvian. The latter is not joined to the orbital sulcus on the right side. In each hemisphere there are two horizontal prorean sulci in front of the orbital sulcus. There is also an extensive vertical sulcus parallel to the sulcus B, near the posterior margin of the hemisphere. (Ziehen describes a brain of Macropus rufus. Jena. Denkschr., Bd. vi. 1897, p. 54.) 212. The brain and the upper portion of the spinal cord of a Giant Kangaroo {Macropus giganteus). This is the largest brain found in any existing Marsupial, although the extinct forms Thylacoleo and Dijyrotodon possessed brains of much greater size. In this specimen the large olfactory bulbs are missing, but the size and shape of these parts of the brain are well shown in the casts of the cranial cavity (D. 215). The orbital (presylvian) sulcus and the sulci A and B all spring from the rhinal fissure. The sulcus B on the left side Joins the suprasylvian sulcus, and the latter extends almost as far forward as the orbital (presylvian). A prorean sulcus is present. On the right side there is an additional sulcus between the sulci A and B, and the orbital sulcus is small. It is a strange fact that the " paramedial " sulcus (compare fio- 58) which is such a characteristic feature of all other representatives of the Macropodidae, is lacking in this, the largest member of the family. n , . Behind the sulcus b there are a number of small sulci, which on the whole assume a vertical (transverse) direction. The characteristic features of the base of the mammahan brain are exceedingly clearly demonstrated in this specimen (fig 57) Note especially the thin-walled pouch of the infundibulum, from which the pituitary body has been torn away. NERVOUS SYSTEM. — VERTEBRATA. 179 The cerebellum conforms to the type presented by the smaller Marsupials, but the folia are much more numerous. In most other Orders of mammals we find in the larger members that the cerebellum becomes more compact, and the region behind the primary (preclival) fissure ceases to assume the hood-like form covering the anterior lobe. As a result of the slighter degree of expansion of this part of the cerebellum in such mammals, the exposed medullary area becomes greatly reduced, or even disappears. But in the Kangaroo this does not happen. The type of the Fig. 57. (x|.) smaller members of the Order with a hood-like covering for the anterior lobe and exposed medullary areas is re- tained, as it is in the Thylacine ; and the only diff'erence consists in the larger size of the organ and a richer supply of fissures, and consequently more numerous folia. 0. 0. 1323 A a. Ziehen, Jena. Denkschr., Bd. vi, 1897, p. 54. D. 213. The left cerebral hemisphere, optic thalamus., and part of the mid-brain of a Giant Kangaroo {Macropus giganteus). There is a typically prolonged calcarine sulcus, and the genual and rostral sulci are joined. There is a well-developed sulcus A— the " Sylvian fissure'' of most writers. The sulcus B, the " suprasylvian " sulcus, and the " coronal " sulcus are joined to form a large arc. There is a large presylvian sulcus. n2 180 PHYSIOLOGICAL SERIES. The cephalic portion of the fascia dentata and the characteristically bilaminar dorsal commissure of the Macro- podidae are well demonstrated. 0. C. 1323 a i. D. 214. The right hemisphere o£ the same brain of the Giant Kangaroo {Macropus giganteus) as specimen D. 213, cut transversely through the two cerebral commissures. Upon the mesial surface of the hinder [lower in bottle] fragment the arrangement of fascia dentata and fornix typical of the Marsupialia, and already described in the Black-faced Kangaroo, may be seen. The features of a coronal section through the commissures are seen, perhaps, to better advantage than in speci- men D. 209. 0.0. 1323 A ^. D. 215. A cast of the cranial cavity of a Giant Kangaroo {Macropus giganteus). [In duplicate,] This cast shows the true shape and proportions of the largest brain of an existing Marsupial, and permits us to compare the impression of the interior of the cranium with actual brains of the same species. We are thus able to appreciate to how great an extent we can rely upon casts of the cranial cavity in the interpretation of the features of the brain in such extinct forms as Thjlacoleo. The shape of the large projecting olfactory bulbs is shown more accurately than in the other specimens. This peculiar form of bulb occurs also in all the Lemuroidea and in many Ungulates. Note also the pronounced ventral extension of the postsylvian area of neopallium and the very marked tapering of the anterior poles of the hemi- spheres The relation of the hemispheres to the cerebellum, olfactory bulbs, and the pituitary body is very strikingly demonstrated. It will be seen that from such a cast as this it is possible to map out the pattern of the cerebral sulci with almost as much certainty as in the actual brain. Thus we see the deep orbital and the shallower prorean sulci, just as clearly as in specimen D. 211. The two pseudosylvian sulci diverging from the angle of the rhmal are also clearly exposed. The great V-shaped sulcus which NERVOUS SYSTEM. — VERTEBRATA. 181 I tentatively called " suprasylvian " is also seen to consist of two limbs. Of these the posterior (as a study of this series of Macropod brains shows) is much the more stable and represents in all, probably, the suprasylvian sulcus o£ other Orders, in spite o£ the fact that its topographical relations are so peculiar. The anterior limb of the V may represent the coronal sulcus of the Carnivora and Ungulata. We can also see a transverse sulcus extending inward from the angle of the V, just as we sometimes find in the actual brain (see D. 211). It is interesting to note that there is a large shallow depression in the place of the lateral (" para- medial ") sulcus — a fact which is not demonstrable in the actual brains. This is of great interest when the peculiar absence of this sulcus in the larger, and not in the smaller, Macropods is recalled. There is a deep, long, postlateral sulcus. D. 216. The brain of a Parry's Wallaby [Macropus parryi) . A . short deep " Sylvian fissure " — sulcus A — extends almost vertically upward from the bend of the rhiual fissure (figs. 58 and 59). Fig. 58. (Nat. size.) The orbital (presylvian) sulcus and the sulcus B both spring from the rhinal fissure, and diverge widely as they ascend. On the left hemisphere the short extent of the true orbitnl sulcus is seen, because it is not joined to the 182 PHYSIOLOGICAL SERIES. false orbital. [This is not shown in fig. 59, wliicli represents the condition found on the right hemisphere reversed.] The suprasylvian sulcus is connected neither with the sulcus B nor with the orbital. As in the Thylacine, the prorean sulcus joins the orbital on the right side only. Fig. 59. (Nat. size.) SULC.ORB. SULC.SUPRAS. On the caudo-mesial angle of the dorsal surface the characteristically Macropod paramedial sulcus is found (fig. 58). It probably represents the earliest form of the sulcus called " lateral " in Carnivores and Ungulates and " iutraparietal " in Primates. There are two fragments (d and d') of a vertical sulcus behind the sulcus B. 0. 0. 1323 A c. D. 217. A rough dissection of the brain of a Macropus. On the right side almost the whole of the cerebral hemisphere has been removed. On the left side the roof of the hemisphere and the greater part of the hippocampus have been removed in order to expose the fornix (fimbria) proceeding obliquely across the optic thalamus to the dorsal commissure. The nucleus caudatus is also exposed in the left hemi- sphere. This dissection was made by the late Sir Richard (then Professor) Owen for his memoir in the Phil. Trans. 1837. 0.0. 1323 A.. D. 218. The brain of a Bennett's Wallaby (Macropus rujicollis). The general features of this brain resemble those of Parry's Wallaby (D. 216). The arrangement of the sulci in this species is interesting because it is intermediate between that of the Kangaroo NERVOUS SYSTEM. — VERTEBRATA. 183 and the smaller Macropods. The arrangement of the three sulci which diverge from the region of the angle of the rhinal fissure is identical with that of the Giant Kangaroo. But there is a sulcus, the " paramedian/' springing from the postero-superior part of the great arc formed by the supra- sylvian and sulcus B, which is not represented in the Kangaroo's brain. It proceeds obliquely backward to the postero-mesial corner of the upper surface. This sulcus is seen in its typical form on the left hemisphere only : on the right side two small sulci take its place. The interest attaching to the paramedian sulcus is that it is a very characteristic feature of the smaller Macropodidse. O. C. 1323 Kh. Ziehen, Jena. Denkschr., Bd. vi. 1897, p. 71. [In Ziehen's specimen the sulcus A, his i/r, is much more imperfect than in this specimen.] D. 219. The brain of a Derbian Wallaby {Macropus derhianus). This is not unlike the brain of Bennett's Wallaby. The cerebral hemispheres have been separated from above in order to expose the dorsal or hippocampal com- missure, which may be seen as a narrow transverse band in front of the third ventricle. 0. C. 1323 A li. Ziehen, Jena. Denkschr., Bd. vi. 1897, p. 71. D. 220. The brain of Rat-Kangaroo [Bettongia gaimardi) ( ? ). The pallium is almost devoid of sulci, and in shape not unlike that of the Phalangers. There is, however, on the caudo-mesial angle of the dorsal surface the characteristic paramedian sulcus of the Macropodidse. This sulcus prob- ably represents the " lateral sulcus " of the Rodents, Ungulates, and Carnivores. 0. 0. 1323 A 5^. Gervais, Nouv. Arch. Mus., t. v. 1869, p. 240. D. 221. The brain of a Tree-Kangaroo (Dendrolagus inustus) ( ? ), in which the left hemisphere has been separated from the rest of the brain. The olfactory bulbs have been removed. In shape the cerebral hemispheres and the cerebellum conform to the Macropod type. But the hemisphere is remarkable for PHYSIOLOQIOAL SERIES. the paucity of sulci. There is a short sulcus a Sylvian fissure ") on the right side, hut it is almost completely aborted on the left side. There is a short deep paramedian, the characteristic Macropod, sulcus ; and also a small prorean sulcus. No other sulci are found on the cranial surface. But there are a number of shallow ill-defined depressions which conform to no known pattern. On the mesial surface there is the characteristic, oblique, prolonged calcarine sulcus and a more characteristic inter- calary sulcus than is usually found in Marsupials. The features of the cerebellum, and in fact of all parts of this brain, are demonstrated with exceptional clearness. 0. C. 1323 A^?. Beddard, Proc. Zool. Soc. 1895, p. 136. Family PhascolomyiduE. 222. The brain of a Wombat {Phascolomys ursinus), in which the left hemisphere has been separated from the rest of the brain. The short, broad, blunt anterior extremities of the hemi- spheres of this brain form a marked contrast to the pointed anterior poles of most other large Marsupials, such as the Kangaroos and especially the Thylacine. The cerebral sulci are in many respects pecuHar. Per- haps the most significant feature is the absence of a well- defined calcarine sulcus, which is such a constant feature in the Marsupiaha, and also in the Eutheria with the ex- ception of the peculiar Order of Rodents. A typical orbital (presylvian) sulcus, such as we find in the Carnivora, appears to spring from the rhinal fissure far forward near the olfactory bulb. It is prolonged back- ward under a small operculum, which meets the lower (pyriform) lip of the rhinal fissure, and then appears to curve upward again in what may be called the Sylvian region (fig. 60, a). This apparent upturned caudal ex- tremity of the orbital sulcus, which may be regarded as the representative of the sulcus a of the Kangaroos, presents a close resemblance to the arrangement found in many Viverrida (e.g. the Civet, vide infra). [A com- parison with the latter will indicate why the two sulci a and NERVOUS SYSTEM. — VERTEBRATA. 185 B of the Kangaroo were spoken of (supra) as representing the so-called " Sylvian fissure " of the Carnivora.] Behind the stilcus A there is a short deep sulcus B pi-o- ceeding obliquely upward and backward from a triangular depression at the bend of the rhinal fissure. Fig. 60. (Nat. size.) SULC . SUPRAS. OLF.'SULB. RHIN.F. Above the sulcus A there is a long oblique suprasylvian sulcus (figs. 60 & 61). As this sulcus is directed upwurd and backward, it resembles the typical suprasylvian sulcus Fig. 61. (Nat, size.) SUUJ. p. LAT. (e. g. in the Carnivora) much more closely than that of the smaller Macropods {e.g. Parry's Wallaby, fig. 59), the obliquity of which is upward and forward *. * This difference may possibly be associated with the pronounced dwindling of the anterior regions of the hemisphere iu the Macropodidte. 186 PHYSIOLOGICAL SERIES. To the mesial side of this suprasylvian sulcus there is a " lateral " sulcus placed midway between the anterior and l)osterior extremities of the hemisphere. It is widely separ- ated from its morphological posterior extremity (fig. 61, b), which is a notch on the caudo-mesial angle. The latter may be regarded as the representative of the paramedian sulcus of the Kangaroos. On the right hemisphere it is joined to a long transverse " post-lateral " sulcus. The small sulcus F (fig. 60) may represent the postsylvian (posterior suprasylvian) sulcus of other Orders. There is a small separate prorean sulcus (fig. 61), and behind it there is a short transverse sulcus G, which may represent the coronal sulcus of other Orders. On the mesial surface (fig. 62) the typically Marsupial arrangement of commissures and hippocampal formation is Fig. 62. (Nat. size.) CQMM . D '■•RHIN . F. seen. The dorsal commissure is not elongated to the same extent as in the Kangaroos, so that it more closely resembles tliat of the Polyprotodont Marsupials. The prolonged genual sulcus is like that of the Kangaroo, as is also the rostral sulcus. There is also the most extraordinary ab- sence of the calcarine sulcus, in place of which there is merely a small irregular pit (h). Lower down we find a short horizontal sulcus above the rhinal fissure (fig. 62). 0.0. 1323 An. B. Owen, Todd's Oyclopsedia, 1847, vol. iii. p. 293. W. H. Flower, Phil. Trans, vol. civ. 1865, p. 646. D. 223. Two casts of the cranial cavity of a Wombat {Phasco- omys ur sinus). These casts admirably show the broad flattened cerebral NERVOUS SYSTEM. — VEBTEBRATA. 187 hemispheres and the projecting olfactory bulbs, as in the Kangaroos. The cerebral sulci are very deep furrows, conforming to the same pattern as in the brain (D. 222). Gervais, Nouv. Archiv. Mus., t. v. 1869, p. 235. D. 224. The brain of a Wombat {Pliascolomys ursinus), dissected to expose the dorsal or hippocampal commissure from above. This dissection was made by the late Sir Richard (then Professor) Owen to demonstrate that the dorsal commissure of the Marsupial is derived from the fornix, i. e. that it is a hippocampal commissure or psalterium (Phil. Trans. 1837, p. 90; also Todd's Cyclopaedia, vol. iii. p. 294, fig. 117 ; also 'Anatomy of Vertebrates,' vol. iii.). The greater part of the cerebral hemispheres has been removed so as to expose the upper surface of the dorsal commissure, which may be seen passing into the fimbria upon each side. On the right side the fascia dentata may be seen lying upon the fimbria and extending obliquely across the upper surface of the dorsal commissures so as to reach the mesial surface of the hemisphere in front of the commissure. The corpora striata have been exposed in the lateral ventricles. Part of the cerebellum has been removed so as to open up the fourth ventricle. 0. C. 1323 A o. Family Phalangerid^. D. 225. The brain of a Brown Phalanger ( Trichosurus fuliginosus) . In general appearance this brain is not unlike that of the Rat-Kangaroos. It exhibits a shallow depression in the situation where the characteristic paramedian sulcus occurs in the smaller Macropodidse. Traces of a prorean sulcus and that called " suprasylvian " in the Kangaroo are present. Although the neopallium is much larger than that of many of the smaller Polyprotodont Marsupials which possess a well-defined orbital sulcus, the latter feature is not clearly defined. 0. C. 1323 Am. Ziehen, Jena. Denkschr., Bd. vi. 1897, p. 84. 188 PHYSIOLOGICAL SERIES. D. 226. The brain of a Flying Phalanger (Petaurus breviceps). In all respects like a small specimen of Trichosurm. [The olfactory bulbs are lacking in this specimen.] O.C. 1323 Bc. Gervais, Nouv. Arch. Mus., t. v. 1869, p. 243. D. 227. The brain of a Koala or Australian "Native Bear" (^Phascolarctus cinereus) ( c? ) . The most noteworthy feature of this brain, as in Dendro- lagus (D. 221), is the paucity of sulci in such a relatively large neopallium. The few sulci which are found are exceedingly variable, and it becomes very difficult to determine their homologies with any certainty. The most pronounced sulcus (in this specimen) ascends from about the mid-point of the rhinal fissure, and may possibly represent the Carnivore pseudosylvian sulcus. In many cases, however, it is quite insignificant and does not join the rhinal fissure. In such cases there is often a much deeper sulcus behind it, which Ziehen calls " Sylvian." In front of these pseudosylvian sulci there is a very faintly marked orbital (presylvian) sulcus. In addition very shallow furrows traverse all parts of the neopallium. The dorsal commissure is very small. The hippocampus presents the typical Marsupial arrangement. There is a short calcarine (splenial) sulcus, which cannot be seen in this specimen. 0. 0. 1323 A r. Ziehen, Jenaische Denkschr., Bd. vi. 1897, p. 98. • Elliot Smith, Journ. Anat. &Phys.,vol. xxxiii. 1898,p. 30. D. 228. The brain of a Koala (PJiascolarctus cinerexis), ( ? ). The sulci are much more imperfectly developed in this specimen. There is a pseudosylvian sulcus on the left hemisphere only. 0- ^ 1323 a s. D. 229. Casts of the cranial cavities of two skulls of the extinct Thylacoleo carnifex. The same peculiar, broad, flattened shape which charac- terises the brain ol Phascolomys is also presented by these NERVOUS SYSTEM. — VERTEBRATA, 189 two casts. The brain, however, was much larger than that of any living Marsupial, being about as large as that of a Pig, Hysena, or Entellus Monkey. It possessed very large olfactory bulbs lying almost wholly in front of the hemispheres. There was a very deep vertical " orbital sulcus," resem- bling in position that of Macropus or Phascolarctns rather than that of Phascolomys. A very deep prorean sulcus ; a deep (single), oblique, pseudosylvian sulcus (such as that labelled B in Phascolomys) ; suprasylvian and lateral sulci resembling those of Phascolomys rather than those of Macropus, and a postlateral sulcus are the most striking- features of these hemispherss. Gervais, Nouv. Arch, de Mus., t. v. 1869, p. 236. Order INSECTIVOEA, Family JEniNACEWjU. D. 230. The left half of the brain of a Hedgehog {Erinaceiis europmus), which had been divided by a mesial sagittal section (figs. 63, 64, & 65). Also the left half of another Hedgehog's brain, dissected to show the hippocampus in the lateral ventricle. Fig. 63. (xli.) ■■-OPAl.. RHIN.F. SULC. ORB \ QLF, BULB. OLF. TUBER. This is one of the simplest and most generalised of mam- malian bruins. It closely resembles the brain of the Poly- protodont Marsupials (and especially Perameles) in all points except the arrangement of the cerebral commissures and the hippocampus, because the Hedgehog possesses a small corpus callosum and the Marsupials have none in the true sense. The resemblance between the brains of the PHYSIOLOGICAL SERIES. Hedgehog and the Bandicoot is, however, very close, as a glance at figs. 52 and 65 so clearly demonstrates. In the Hedgehog the olfactory apparatus is extra- ordinarily largely developed, as we might expect in such a lowly mammal of fossorial habits. Fig. 64. (xU.) HIP. CORP. CALL. / CORP. QUAD. QOMM.A. ; CORP. FIS. SOFT COMM. The neopallium is reduced to exceedingly diminutive proportions, so that the rhinal fissure (fig. 63) is placed very high up upon the lateral wall of the hemisphere. Thus the pyriform lobe forms the greater part of the lateral wall. Fig. 65. (Xli) There is a short, very shallow, transverse orliital (pre- sylvian) furrow on the dorsal surface, as in Perameles and Sarcophilus. In the nearly-related and larger Gymnura this shallow furrow becomes converted into a deep sulcus. The fascia dentata makes its appearance upon the NERVOUS SYSTEM. — VERTEBRATA. 191 ventral surface of the hemisphere, on the mesial side of a depressed area corresponding to the nucleus amygdalae. The simple cerebellum is slightly more elaborated than that of Perameles, so that it comes to more closely resemble that of Sarcophilus. It has sessile flocculi (comp. figs. 65 and 52). In the dissected specimen (fig. 66), the lateral ventricle is prolonged forward to communicate by a narrow channel with the large cavity in the olfactory bulb. The hippocampus is placed in the caudal part of the chief cavity, and does not extend so far forward as in the Marsupial (compare the Wallaby's brain, D. 210). The meaning of this is that when the corpus callosum makes its appearance (as it does for the first time in the Eutheria), the cephalic extremity of the Fig. 66. (xli.) □LF . VENT hippocampus becomes reduced to a mere vestige lying partly upon the upper surface of the corpus callosum and partly in front of the latter body. • The existence of a corpus callosum and the vestigial nature of the anterior part of the hippo- campal arc are the great distinguishing features of the Eutherian brain, when compared with that of Marsupials and Monotremes. Flatau and Jacobsohn, Vergl. Anat. d. Centralnerv. 1900, p. 341). Ganser, Morph. Jahrb., Bd. vii. 1882, p. 591. Elliot Smith, Journ. Anat. & Phvs., vol. xxxii. 1897, p. 44. D. 231. A cast of the cranial cavity of a Hedgehog {Erinaceus europceus) . Shows the exact size and shape of the cerebral hemi- spheres and olfactory bulbs. 192 PHYSIOLOGICAL SKRIRS. Family Talpwm. D.232. The brain o£ a Mole {Talpa europcea) (?), exposed in situ. This simple, highly macrosaiatic brain resembles that of the Hedgehog but shows signs of greater specialisation. It is, however, smaller, more flattened, and the optic parts of the brain are very poorly developed. Ganser, Morph. Jahrb., Bd. vii. 1882, p. 591. Family Tupaiid^. D. 233. A cast of the cranial cavity of a Tupaia ( Tupaia tana). Family GentetidjE. D.234. The cast of the cranial cavity of a Tenrec {Centetet ecaudatus) . The olfactory bulbs are even larger in proportion to the size of the brain than they are in the Hedgehog. Such brains as those of Centetes and Erinaceus enable us to appreciate the characters of the earliest Eutheria, and such forms as the Eocene Ungulate Dinoceras. In the case of Centetes, however, the small size of the hemispheres is largely a secondary retrogressive change which occurs in the development of each individual (Forsyth Major). Suborder Dermoptbra. Family GaleopjthecjdjE. D. 235. The brain of a Colugo {Galeopithecus volans), which has been divided in the mesial sagittal plane; and the left cerebral hemisphere separated from the brain-stem (figs. 67, 68, 69, and 70). This brain is of great interest because it presents a series of well-defined cerebral sulci, and at the same time exhibits features which justify the lowly status usually accorded to Galeopithecus in the mammalian series. NRUVOUS SYSTEM. — VEUTKBKATA. 193 Thus the small size of the cerebral hemispheres which leave the greater part o£ the corpora quadrigemina exposed; the high degree of macrosraatism in an arboreal animal; the prominence of the hippocampus; the small dimensions of the corpus callosum; and the smallness and primitive simplicity of the cerebellum, all jioint to the lowly status of this peculiar mammal, not far removed from the Insectivora. Fig-. 67. (Nut. size.) Fig-. 68. { Xat. .size.) Fig. 69. (Nat. size.) Fig. 70. (Nat. size.) SULC.CALC. The very definite series of deep sulci on the cerebral hemisphere, however, at once separates Galeopithecus from the Insectivores proper. On the mesial surface there is a relatively small and very obliquely-placed corpus callosum. The large fascia dentata is, to a great extent, exposed on the surface (fig. 69)._ There is a deep calcarine (splenial) sulcus, beginning, as is usual, near the termination of the rhinal fissure and pursuing a course approximately horizontally forward. Its VOL. II. o 194 PHYSIOLOGICAL SKUIES. slightly upturned auterior extremity overlaps the jiosterior extremity of a sulcus curiously like the rostral sulcus of the Sloths (fig. 69). The peculiarly-sinuous rhinal fissure is placed high up on the lateral wall of the hemisphere. Its posterior ex- tremity rises to a much higher level than any other p:irt of the fissure (fig. 68), as often happens also in the Eocene Mammalia. In the small neopallium we find short sulci corresponding to the orbital (presylvian) sulcus (x), and the so-called " Sylvian fissure " (y) of such mammals as the Three-toed Sloth and many Carnivores. Midway between these sulci and the interhemispheral cleft there is a longitudinal sulcus almost as long as the liemisphere, px'esenting a slight concavity toward the mesial plane (fig. G7, w). There is nothing to help us to decide whether it represents either the suprasylvian or the lateral sulcus, unless it be the fact that the former is the more primitive and stable of the two sulci in mammals generally. But its resemblance to the conjoint suprasylvian and coronal sulci in such small Ungulates as Dorcatherium and Iragulus seems to be more than a fortuitous likeness. . The cerebellum is unusually small and presents all the primitive simplicity o£ the Insectivore organ. [The greatly-projecting floccular lobes have become knocked off in this specimen,] The anterior quadrigeminal bodies are extremely large and bulge upward between the cerebellum and the cerebral • hemispheres. The posterior quadrigeminal bodies and the mesial geniculate bodies are of moderate dimensions. It is of interest to note that the tractus peduncuhiris transversus, which is feebly developed or perhaps absent in Marsupials and certain of the Insectivora and Edentata, is well-developed in Galeopithecus. Presented hy Prof. G. Elliot Smith *. W. Leche, Kongl. Sv. Vet.-Alcad. Handl., Bd. xxi. 1886, p. 48. * This is one of several specimens which had beeu extracted and care- fully preserved by Dr. Charles Hose, of Borneo, and generously given to the vriler for examination. NERVOUS SYSTEM. — VERTEBRATA. 195 D. 236. A cast of tho cranial cavity of a Colugo (Galeopithecus volans). [In duplicate.] This cast shows the true shape and proportions of the olfiictory bulbs, cerebral hemispheres, and the main mass of the cerebellum. It gives some idea as to the exact area of the quadrigeminal bodies exposed. The rhinal and "modified suprasjlvian " furrows are well shown. Gervais, Journ. de Zoo!., t. i. 1872, p. 445. Oedee EODENTIA. Section Soitjromorpha. Family Gastomid^. D. 237. The brain of a European Beaver ( Castor fiber). Most parts of the brain of the Rodents present features such as are common to most of the Eutheria ; but in respect to the arrangement of the sulci of the cerebral hemispheres, the Rodentia are the most aberrant group of the Eutheria (excepting perhaps the peculiarly-modified Sirenia). The most noteworthy features in the brain of the Beaver are the obliteration of a great part of the rhinal fissure and the utter absence of sulci in the large pallium. The meaning of this is not altogether clear, but appearances suggest that the growth of the brain in a roomy cranial cavity which has exercised little restraint on the growing hemispheres may explain this absence of sulci and imperfection of the rhinal fissure. But even admitting this, the smoothness of such large hemispheres is a peculiar phenomenon, which is much rarer than is generally supposed. Thus even in the small JBrinaceus, among the primitive Insectivores, there is a well-developed rhinal fissure and distinct traces of at least one neopallial sulcus ; and in Gymnura and, especially, Galeopithecus there are deep sulci, in spite of the fact that these brains are much smaller than that of the Beaver and represent a more primitive type. Then, again, among the Hystricomorphine Rodents we find 0 2 196 PHYSIOLOGICAL SERIES. cerebral hemispheres of the same dimensions as, or even smaller than, the Seiuromorphine Castor, possessing numerous deep sulci. This is one of the enigmas of cerebral morphology which we are utterly unable to satisfactorily explain at present. 0. C. 1328 e. Beddard, Proc. Zool. Soc. 1892, p. 597. D. 238. The brain of a Beaver {Castor fiber), dissected to show the distribution of the fibres of the corpus callosum. This dissection was made by Prof. Richard Owen for purposes of comparison with the brain of the Wombat (D. 224). Its object was to demonstrate by comparison the absence of the corpus callosum in the Marsupial. R. Owen, Phil. Trans. 1837, p. 89. 0. C. 1323 e a. D. 239. The brain of a Beaver {Castor fiber), dissected to show the hippocampus and fornix. This dissection was also made by the late Prof. Richard Owen. By comparison with D. 238, it will be seen that when the corpus callosum has been removed, as in this specimen, an arrangement of the fornix is exposed which is analogous to that which may be seen in the Marsupial (D. 224) without removing any such commissure. Hence, Owen argued, the corpus callosum is lacking in the Marsupial. This rough dissection does not clearly demonstrate the further fact that in the Rodent the hippocampus does not extend forward so far as it does in the Marsupial. 0. C. 1323 e 6. D. 240. The brain of an American Beaver {Castor canadensis), There is a shallow sagittal furrow on the dorsal surface of each hemisphere, which might represent either the corono-lateral or the suprasylvian sulcus. The latter is the more stable and precocious of the two sulci, and is rarely absent when the lateral sulcus exists. Yet we know for certain that this sometimes happens in the case of Tamanduas (Edentata). NERVOUS SYSTEM. — VERTEBRATA. 197 From the position of the sulcus in this specimen and by comparison with the brains of DolicJiotis and Tamanduas, it seems more likely to be a representative of the lateral (or combined lateral and coronary). Note that the corpus callosum is rather short and plump, such as is found in the more primitive Insectivora. 0. C. 1323 e/. D. 241. Two casts of the cranial cavity of an American Beaver {Castor canadensis). Family SciuniD^, D. 242. The right half of the brain of a Squirrel [Sciurus vulgaris) . No sulci are present in the pallium. The corpus callosum is long and narrow with a definite genual thickening. The anterior quadrigeminal bodies are very large, probably because an active arboreal animal needs a well- developed visual apparatus. 0. C. 1323 F. D. 243. The brain of a Squirrel {Sciurus capistratus) . ■ In spite of the large size of the anterior quadrigeminal bodies, they are completely hidden by the cerebral hemi- spheres. 0. C. 1323 F a. D. 244. The left half of the brain of a Squirrel {Sciurus capis- tratus). Observe the large size of the optic nerve, with which the prominence of the anterior quadrigeminal bodies is associated. 0. C. 1323 F c. Section Hystrioomoepha. Family Octodontw^. D. 245. The brain of a Coypu {Myocastor cotjpus), ( ? ). This brain resembles that of the Beaver but is much smaller. The rhinal fissure however is well developed. The pallium is devoid of well-defined sulci, although there is a slight furrow on the caudal surface, possibly representing 198 PHYSIOLOGICAL SERIES. the calcarine (splenial) sulcus. It extends upward so as to slightly notch the dorso-caudal margin of the hemisphere. The corpora quadrigemina are partially exposed. According to Beddard other sulci may be present in the pallium. 0. 0. 1323 e c. Gervais, Journ. de Zool., t. i. 1872, pi. xxiii. fig. 7. (In this memoir cranial casts of numerous Rodents are described.) Family Hystbicid^. D. 246. The brain of a Porcupine {Ilystrix sp.). The cerebral hemispheres are very broad. (Their posterior extremities do not diverge in the manner Beddard describes, and the corpora quadrigemina are quite hidden.) The base of the brain resembles in shape that of the Beaver, but the rhinal fissures are deep and well-defined. There are two chief sulci and several pit-like depressions on the pallium. A short shallow posterior furrow runs parallel to the interhemispheral cleft and resembles the paramedian sulcus of the Kangaroos. There is a longer oblique sulcus further forward which cannot be strictly compared to any sulcus in other mammalian brains. It is impossible to say with any degree of certainty whether it represents the suprasylvian or a lateral element of such a form as the Capybara. There is no Sylvian fissure, although Beddard describes such a fissure in his specimens. 0. C. 1323 e e. Beddard, Proc. Zool. Soc. 1892, p. 600. D. 247. The brain of a (Canadian Porcupine (Erithizon dorsatum) . This brain is much more lilve that of the Coypu than the Porcupine. Its pallium is quite devoid of sulci. 0. C. 1323 E m. Presented by St. George Mivart, Esq. D. 248. The brain of a Mexican Tree-Porcupine (Coenodon mexicanus) . This brain resembles that of the Canadian Porcupine. Its pallium is entirely free from sulci, but is grooved in all directions by vascular furrows. 0. G. 1323 B k. NERVOirs SYSTEM. — VERTEBEATA. 199 Family Ghinchillid^. D. 249. The brain of a Viscacha ( Viscaccia maxima) , in which the right cerebral hemisphere has been dissected to expose the hippocampus from above. There is a vertically-placed, somewhat arched, deep sulcus above the mid-point of the rhinal fissure, but not communicating with it. It may be regarded as the repre- sentative of the sulcus in the brain of Dolichotis (figs. 74, 75, s), which has been called Sylvio-suprasylvian ; in other words, it is the suprasylvian sulcus or the Prosimian Sylvian. In front of this sulcus the hemisphere gradually tapers to a narrow anterior extremity, and behind the sulcus the • hemisphere suddenly broadens. There are two well-marked sagittal sulci representing the corono-lateral complex. According to Beddard other sulci may occur. 0. C. 1323 E /. Beddard, Proc. Zool. Soc. 1892, p. 599. D. 250. The brain of a Viscacha {Viscaccia maxima). 0. C. 1323 G D. 251. The brain of a Common Chinchilla [Chinchilla layiigera). The pallium is apparently devoid of sulci. It is, however, hidden to some extent in this specimen by the membranes, in which the middle cerebral artery is very prominent. 0. C. 1323 E^. Family Dasyproctid^. D. 252. The brain of an Agouti {Dasyprocta aguti). In contradistinction to the flattening which charac- terizes the basal region of the hemispheres in many Rodents, the pyriform lobe and olfactory tubercle in this specimen present the plump, rounded features which distinguish these regions in macrosmatic brains of other Orders. A deep and well-defined sulcus indents almost the whole length of the hemisphere parallel to and a short distance 200 PHYSIOLOGICAL SEllIES. from the interhemispheral cleft. A comparison with the brains of Ori/cteropus, the Anteaters, and Carnivores would lead us to call this the lateral or the conjoint corono-lateral sulcus. Yet it is very unusual to find the lateral sulcus present, and the more precocious and fundamentally stable suprasylvian sulcus absent. If, for instance, we compare this brain with that of Oaleopithecus and many of the smaller Ungulates, the possibility of it being the supra- sylvian presents itself. Taking all its features into consideration, one is inclined to regard it as th(< analogue of the lateral sulcus of such a form as Tamanduas. It is also clear that the anterior extremity of such a sulcus takes the place of the prorean sulcus found in the Marsupialia and Carnivora. Two notch-like indentations in the upper lip of the rhinal fissure may represent the Carnivore pseudosylvian sulcus and the orbital sulcus. Other sulci have been described in the Agouti ; in this specimen shallow depressions occupy the positions of all these sulci. 0. C. 1323 g. Beddard, Proc. ZooL Soc. 1892, p. 602. D 253. The brain of the Paca {Agouti paca). This brain agrees with that of the Agouti in presenting notch-Hke representatives of the orbital and pseudosylvian sulci in the upper lip of the rhinal fissure. The longitudinal (" lateral ") sulcus of the Agouti is here broken up into two fragments— anterior and posterior paramedian sulci respectively, and between them is a short oblique sulcus (which I shall call " ambiguus "), such as the Porcupine exhibits. 0. C. 1323 o b. Beddard, Proc. Zool. Soc. 1892, p. 604. Family CaviidjE. D. 264. The brain of a Capybara {Hydrochoerus capt/bara), in which the left cerebral hemisphere has been separated from the rest of the brain (figures 71, 72, and 73). This brain is much the largest louud in the Rodentia ; NERVOUS SYSTEM. — VERTEBRATA. 201 and in virtue of the great extent of the mantle of the cerebral hemispheres there are numerous sulci. The aberrant character of the Rodent brain is therefore more Fig. 71. (xf.) strikingly exhibited than it is in the smaller and less-richly furrowed brains of the Order. When viewed from above or below the cerebral hemi- spheres present a peculiar lozenge-shape, the lateral edge Fig. 72. (x§.) SUlc.calc. RHIN. F. POST. of each hemisphere being so shaped as to form a projecting angle slightly behind its mid-point. The large olfactory bulbs project freely in front of the hemispheres. 202 PnYSIOLOGICAL SERIES. There is a well-formed corpus callosum with a particularly well-developed genu (fig. 72). The hippocampal formation conforms to the usual Eutherian type. The rhinal fissure however presents peculiar features. It consists of a deep, long horizontal anterior rhinal extending two-thirds of the length of the hemisphere and ending blindly in a triangular depression posteriorly. There is a shallow posterior rhinal fi^ssure which is not joined to the anterior rhinal on the right hemisphere, and is connected to it only by a very shallow furrow on the left (fig. 73). In the region of approximation of these two fissures there is a deep triangular depression, in which Fig. 73. (xj.) i SULC.ORB. SULC.SUPRAS. RHIN.F. the anterior rhinal fissure terminates. Holl has shown that this depression is formed by a sulcus which he calls the ectosylvian. There is a typical presylvian (orbital) sulcus which is placed very far forward and pursues a very oblique, almost horizontal, course, to join Holl's ectosylvian sulcus. The upper lip of the latter sulcus is opercular and meets the lip of the rhinal fissure. The suprasylvian sulcus is deep and oblique, and is often supplemented by a second arcuate element. This second element may be independent (see right hemisphere of this brain), or it may be fused to the true suprasylvian to form a triradiate sulcus (as in the left hemisphere of this and the right hemisphere of the next specimen) . Two sagittal sulci, the longer one placed behind the shorter, extend the whole length of the hemisphere parallel to the interhemispheral cleft. The anterior sulcus probably NEKVOUS SYSTEM. — VERTBBEATA. 203 corresponds to the coronary, and the posterior to the lateral sulcus of other Orders. The adjacent ends o£ both sulci are bifid. There are a number of other sulci on the cranial surface of the hemispheres, but they are so unstable that they differ considerably on the two hemispheres of the brain and to a much greater extent in different brains. It is the sulci (or rather the absence of sulci) on the mesial surface of the Rodent's brain by which the aberrant character of this Order is indicated. The rhinal Hssiu-e extends high up on the mesial surface (of the Capybara's brain) parallel to the hippocampal fissure. The most striking fact, however, is the insignificant representative of the calcarine sulcus. There is only a small sulcus behind the splenium of the corpus callosum in the situation where we should expect the deep long calcarine sulcus. In most Rodents even this is missing, and in this brain the features of this small furrow are such as to render its homology somewhat questionable. But even granting that this sulcus in the Capybara is the true calcarine, its insig- ficance is very peculiar when we recall that in all other Eutherian Orders as well as in the Metatheria the deep, long calcarine sulcus is the most constant and best defined of all the sulci of the neopallium. In the Capybara again, as in all Rodents, there is no intercalary sulcus, if we except the insignificant furrow near the upper surface of the splenium. There is, however, a well-defined genual and also a large rostral sulcus. The cerebellum is remarkable for its small size and compactness (fig. 71). Its folia are arranged in a simple transverse pattern, and as a result there is a close resemblance to the type prevalent in the Ungulata. There is a large floccular lobe. 0. C. 1323 G d. Beddard, Proc. Zool. Soc. 1899, p. 798. Holl, Arch. f. Anat. und Phys. (Anat. Abth.) 1900, p. 295. D. 255. The brain of a Capybara {Hydroclmrus cafyhara) ( ) , in which the left hemisphere has been dissected to show the corpus callosum. 204 PHYSIOLOGICAL SERIES. On the left hemisphere of this brain the peculiar characters of the rhinal fissure are very pronounced. The anterior part of the anterior rhinal fissure is so faintly marked, that the deep posterior part appears to be a back- ward extension of the orbital sulcus. It is separated by a wide interval from the posterior rhinal fissure. Note the peculiar lozenge-shape of the brain. This is well shown in a figure of Retzius^s (Biolog. Untersuch., Bd. viii. 1898, Taf. xii. fig. 1). 0. C. 1323 Ga. D. 266. A cast of the cranial cavity of a Capybara {Hydro- chcerus capybara). [In duplicate.] This shows the true shape and proportions of the large projecting olfactory bulbs : and the peculiar lozenge- shape of the brain as a whole, each cerebral hemisphere having a most pronounced lateral angle slightly behind a point midway between the anterior and posterior poles. Note also the exceedingly small relative size of the cerebellum. Gervais, Journ. de Zool., t. i. 1872, p. 456. D. 267. The brain of a Patagonian Cavy {Dolidiotis magellanica) ( ? ), from which the left cerebral hemisphere has been separated (figs. 74 & 75) . This brain is not so strikingly aberrant as that of the Capybara. And yet the practical absence of well-defined sulci on the mesial surface shows that this peculiarity of the other Rodentia also occurs in this genus. There is however a faint trace of a genual sulcus and a shallow depression where one would expect to find the calcarine sulcus. Unlike that of the Capybara, the brain of this Cavy presents a typical well-defined rhinal fissure, such as is seen elsewhere in the Rodentia, in the Rabbit for instance. There is an extensive sagittal sulcus parallel to and coextensive with almost the whole length of the inter- hemispheral cleft. This corresponds to the corono-lateral sulcus of the Carnivora and Ungulata, and possibly also to the prorean sulcus fused to the coronary element. A great vertical sulcus (s) pursues a slightly arched course upward from the junction of the anterior and posterior NERVOUS SYSTEM. — VEKTBBllA'i'A. 205 rhiiial fissures. It probably represents u fusion of the so-called "Sylvian fissure'^ of most non-Primate orders and the suprasylvian sulcus. Such a fusion is found in the Great Anteater's brain (vide infra) and also, in all probability, in the Primates, in which the complex forms the true Sylvian fissure. In this brain, so as to avoid confusion, we may call it the " Sylvio-suprasylvian complex." rig. 74. (x-g.) There is a small horizontal presylvian (or orbital) sulcus, which is not joined to the rhinal fissure. There is also a short sulcus of doubtful significance on the external side of the caudal end of the lateral sulcus (figs. 74 & 75). Fig. 75. (x§.) SULC.ORB. The resemblance between the cerebral sulci of this brain and those of the Lemurs is very instructive (vide infra). There is a compact cerebellum, which is relatively larger and broader than that of the Capybara. It also conforms to a more generalized type found in many other Hodents, I^jdentates, Insectivores, and Marsupials. The fioccular lobes project like those of the Eabbit. ^ , , , O.C. 1323 -t3eddard, Proc. Zool, Soc. 1802, ji. (iOS. 206 I'HYblOLOtilCAL SICIUE«. Section Myomoupha. Eamily Djpodid^. D. 258. The bniin of a Jerboa [Dipus sagitta). A simple smooth brain presenting no distinctive features. 0. C. 132.3 B^. Family Mubjdm. D. 269. The brain of a Rat [Mus rattus), in which the left hemisphere has been in great part removed to show the niid-brain, and the right hemisphere has been dissected to show the hippocampus. The typical arrangement of the lowly mammalian cerebellum is well shown. 0. C. 1323 F d. D. 260. The brain of a Rat (Mus decumanus). Suborder Duplicidentata. Family Lepobjdje. D. 261. The head of a foetal Hare {Lepus curopcms) with the brain exposed in situ. 0- ^- ^^^^ D. 262. The brain of a Hare (Lepus europceus). 0. C. 1323 G./'. D. 263. The brain of an English Wild Rabbit (Lejius cimiculus). The only trace of sulci in the pallium is a shallow posterior paramedian (lateral) sulcus. 0. C. 1323 G e. Presented by H. Power, Esq. Flatau and Jacobsohn, Vergl. Anat. d. Gentralnerv. 1900, p. 351. D. 264. The left cerebral hemisphere of a Rabbit (Lepus cuui- culus), dissected to show the hippocampus (fig. 70). Fig. 76. (Nat. size.) OLF.SULB Beincr a larger brain, this shows more clearly than the Hedgehog's brain the difference between the Euthenan and NEKVOUS SYSTEM. — VBIiTEBUATA. 207 Mctiitheritin hippocampus. The Rabbit's hi]ipocanipiis is restricted to the caudal part of the ventricle and does not extend so far forward as that of the Wallaby (D. 210). Note the continuity of the lateral ventricle with the cavity in the olfactory bulb. D. 265. Two casts of the cranial cavity of a Rabbit (Lepus cuni- Order CHIEOPTERA. D. 266. A cast of the cranial cavity of a Rousette Bat {Fteropus vainpyrus). The brain in the Chiroptera exhibits features which indicate its lowly status in the mammalian series. It does not show signs of any marked specialisation or divergence from the primitive type of the Insectivora. The hemisphere is peculiar in that the rhinal fissure is almost completely deficient, although the well-developed j)yriform lobe and neopallium present typical features. In the small bats the minute cerebral hemispheres are separated by a wide gap from the cerebellum so that almost the whole of the corpora quadrigemina is exposed. These hemispheres are, of course, quite smooth. In the larger forms, such as Cynonycteris, there is a well-develo]jed splenial complex of calcarine and intercalary sulci of the typical form. In the largest representatives, such as Pteropus, this splenial arc becomes even more extensive. On the cranial surface there is in Cynonycteris a very short, deep suprasylvian sulcus and a small shallow lateral sulcus. The latter may in some cases become deeper and more extensive. In this cranial cast of Pteropus there is a short, deep, suprasylvian and a short, shallow, lateral sulcus. There is no orbital sulcus, nor is there any trace of a pseudosylvian sulcus. In the larger Bats the cerebral commissures are well- developed and resemble those of Galeopithecus. But in many of the smallest Bats (e. g. JS'yctopJdlus and Vespertilio) the corpus callosum becomes extremely reduced in size so 208 PHYSIOLOGICAL SKRIRS. that tlio commissures present u spurious resemblance to those o£ the Mursupialia (Trans. Linn. Hoc. vol. vii. ])t. 8. 1897, p. 47). The cerebellum and the other |)arts of the brain closely resemble the corresponding organs in Galeopithecus. In the small Bats the enormous development of the auditory tracts is specially noteworthy. Flatau and Jacobsohn, Vergl. Anat. d. Centralnerv. lyOO, p. 208. Gervais, Journ. dc Zool., t. i. 1872, ]). 437. Also Retzius, Leche, Elliot Smith, and others. Order EDENTATA. Family Basvpodw^. D. 267. The brain of a Six-banded Armadillo {Dasypus sexdnctus). This is a simple, highly macrosmatic brain resembling that of the generalised Insectivores in most of its features. The rhinal fissure, however, consists of two fragments separated by a wide gap (fig. 77). The posterior of these Fig. 77. (Nat. size.) (uHiN.F.rosT.) is prolonged obliquely forward into con- tinuity with a sulcus (/3) of the neoi^allium, which i)robably corresponds to the orbital or presylvian sulcus of other mammalian brains. Above the posterior rhinal fissure there is a second oblique sulcus (8) in the neopallium, which may be regarded as the representative of the suprasylvian sulcus of the Carnivora or of the Myrmccophagidiv. NERVOUS SYSTEM. — VBRTEBRATA. 209 On the mesial surface of the hemisphere there is a sulcus which may possibly represent a highly placed calcarine, which has become prolonged forward after the manner of the so-called ''splenial" sulcus of Krueg in most mammals. The appearance of the diminutive corpus callosum (c.c.) and the large hippocampal commissure (ps.d., ps.v.) and anterior commissure (a.c.) are shown diagrammatically in the accompanying scheme (fig. 78), which also exhibits the SPL relations of the fornix or fimbria (f), the fascia deiitata (f.d.), hippocampus nudus (n.h.), and vestigial hippo- campus (v.H.) to the commissures and precommissural area(p). 0. C. 1323 i. Elliot Smith, Trans. Linn. Soc. (2nd Series, Zool.) vol. vii. 1899, p. 297. D. 268. The brain of a Cabassou {Cabassoiis imicinctus). This is an excellent example of a simple, highly macros- matic brain essentially similar to that of the Six-banded Armadillo, but relatively much shorter and broader than the latter. The large olfactory bulbs are flattened against the anterior surface of the short cerebral hemispheres (figs. 79, 80, 81). The posterior rhinal fissure is represented only by a very shallow depression (fig. 80), but the supposed representative of the orbital sulcus is exceedingly well developed (tigs. 79 and 80). The representative of the sulcus S of Dasypxis is much more insignificant in Cahassous (figs. 79 and 80) than it is in the former. VOL. n. p PHYSIOLOGICAL SKIUKS. There is a small corpus callosum and largo psalterium (fig. 81), as in Dasypus (compare fig. 78) ; and the vestiges of the siipracallosal and precallosal parts of the hippocampal Fig. 79. Fig. 80. (Nat. size.) SULC. ORB. RHIN. F. ANT Ot-FTUB Fig. 81. (Nat. size.) A H1P.V£ST.- OtF.BULS. ... ;^REA PRECOM HIP. INV. OLF. TUBER. arc are exceptionally clearly demonstrated (fig. 81). The arrangement of these parts agrees with that shown diacrrammatically for Pasnpus m fig. ^8. NEEVOUS SYSTEM. — VERTEBRATA. There is a very well-developed " splenial " sulcus, pro- bably representing the conjoint calcarine, intercalary and genual sulci of other mammals. It extends much further forward than the analogous sulcus in other Armadillos. ^ The features of the typical, primitively simple mamma- han cerebellum are unusually clearly shown in that of Cabassous (figs. 82, 83, 84, & 85). It closely resembles Fig. 82. (Nat. size.) Fig. 83. (Nat. size.) LOB. CENT. — PARAFLOO. PYRAMID LOa. POST ^PRlM.F. AREA C. FLDC '■PONS.VAROL. Pig. 85. (Nat. size.) PRjur. p. AREA C AREA A. PARAFLOO. LOB. POST. FLOC. ,— AREA B. ■PARAFLOO. LOB. ANT. = Lobus Centralis +Lobu8 culminis. AHEA A=Lobus clivi. ABEA B=Lobus cacuminis. CORP, PUAD. ABEA c=Lobus tuberis. x=Lobus biventralis+ Amygdala. LOB. POST. = Uvula +nodulus. that of the Rabbit exceptithat the large cake-like floccular lobe (composed of flocculus and paraflocculus) is here sessile and flattened against the rest of the cerebellum. Jlilliot bmith, Trans. Lmn. Boc, vol. vii. 1899, pp. 321 & 371. ' D. 269. The brain of a Three-banded Armadillo (Tolypeutes tncinctus). This brain is like that of Cabassous, but is smaller. The suprasylvian sulcus is absent, the orbital (presylvian) sulcus P 2 212 PHYSIOLOGICAL SEllIBS. is shorter There is no pallial sulcus on the mesial surface o£ the left hemisphere, bat a faintly marked furrow is present above the corpus callosum in the right side. 0. C. 1323 I h. Elliot Smith, Trans. Linn. Soc. loe. cit. D 270 The brains of two Pebas ( Tatu novemcincta) . In most of their features these brains closely resemble that of Cabassous. Fig. 86. (Nat. size.) BHIN F. POST. RHIN.F. ANT. ^PARAFLOn. OLF.BULB The posterior rhinal fissure is very small and the anterior rhinal is also very short. There is a well-defined presylvian (B) but no suprasylvian sulcus. The most noteworthy feature is the large size of the corpus callosum in comparison with that of other ^^^-^dillo^^ Elliot Smith, Trans. Linn. Soc. loc. cit. Pamily Qlyptodontid^. D 271. A cast of the cranial cavity of Glyptoion c!a«o^«. This is a replica o£ Qervais's model. It *o,.s the extraordinarily small si.e of the brain in comparison with that of the body of the animal ; the enormous dmren.on of the large, pednnculated and projectmg oMacto.j bulbs , the diminutive si.e of the cerebral hemispheres ; and he extraordinary greatness (especially m breadth) of the %te"rebral hemispheres are flattened, and the only trace of a sulcus is one in the " Sylvian region," «hieh probably r presents the so-called suprasylvian sulcus of the Arma- dlos unless, after the analogy of Gako,nUuc. and many Eocene Mammals, it is a phenomenally ngh r una, fissure. Gervais, Nouv. Arch. Mus., t. v. 1»69, p. ii. NERVOUS SYSTEM. — VERTE.BRATA. 213 D. 272. A. cast oF the cranial cavity of Glyptodon claviceps (two specimens). This is a less perfect cast of a larger brain than D. 271. Family Bhadypodw^. D. 273. The brain of a Three- toed Sloth {Brady pus tndactijlus). [This specimen, having been preserved in situ in the cranium, exactly retains its normal shape, but is unfortu- nately too soft to permit the arachnoid and pia membranes to be removed. The latter, however, are sufficiently thin to permit the sulci to be distinctly seen.] The contrast between this brain and that of an Armadillo is almost as pronounced as are the differences exhibited in a comparison of the brains of the Cat and the Hcdirehoo-. Lhc contrast between the habits of the fossorial, terrestrial PHYSIOLOGICAL SEUIES. Arniadillo and the arboreal herbivorous Sloth sufficiently explain the fact that the former is much more highly macrosmatic than the latter. In the Sloth the neopallium is, in comparison with that of the Armadillo, very large, although it is considerably smaller than that of Carnivores of the same size. It vig.m. (x2.) CORP. CAL. a TELA HIP. VEST. AREA PRECOM OLF. TUBER. COMM. ANT. opt.tr' i VEMT. HI Fig. 90. SPL. is moreover richly supplied with deep sulci, which con- form to a pattern curiously like that which prevails among the Carnivora. The cerebral hemispheres are sufficiently large to huie the corpora quadrigemina and to overlap the cerebellum to some slight extent ; it also partly overhangs the olfactory bulbs (fig. 87) but no olfactory sulcus is developed. On the ventral surface the posterior part of the pyriform lobe forms a very pronounced protuberance, commonly NERVOUS SYSTEM. — VERTEBRATA. 215 known as the " natiform eminence," and as a result of this prominence there is a deep vallecula Sylvii separating the latter from the anterior part of the pyriform lobe and the olfactory tubercle. In profile the brain presents a general resemblance to the Feline type, although there are many differences. The cerebral hemispheres of the Sloth are, in comparison with those of the Cat, much more highly raacrosmatic ; or, to express the same fact more accurately, the neopallium is relatively smaller in the Sloth. The anterior and posterior rhinal fissures meet in an upwardly-directed arc, and the resultant conjoint fissure is placed wholly upon the lateral aspect of the hemisphere and on a much higher plane than the corresponding fissure in the Cat's brain. A distinctive " Sylvian fissure " of the Feline type springs from the apex of the rhinal arch and ascends with a slight backward inclination for a short distance (fig. 87, p,). There is a deep sulcus (/3) which clearly corresponds to the presylvian (or orbital) sulcus of the Carnivora. It pursiTes a horizontal course across the blunt cephalic pole of the hemisphere. Its mesial extremity (fig. 89, /8).is pro- longed on to the inner face ; this mesial prolongation may possibly represent a rostral sulcus. Its lateral extremity does not quite reach the rhinal fissure in this specimen (fig. 87, ^), but in some cases it joins the rhinal fissure and presents relations to the latter and to the Sylvian fissure not unlike the arrangement found in the brain of Galeopithecus. There can be little doubt as to the homology of the arcuate sulcus 8 (figs. 87 & 88) with the combined supra- sylvian and postsylvian sulci of the Carnivora. The anterior limb of this suprasylvian arc (so we may call it) is very short. There is a short horizontal branch from the posterior part of the arc such as is often found in an analo- gous situation in the Carnivore's brain. There is a very small diagonal sulcus (compare the Cat's brain) in front of and slightly below the suprasylvian arc. There is a sagittally-directed sulcus (7) analogous to that called " lateral " in the Carnivora ; it pursues a course 216 PHYSIOLOGICAL SERIES. parallel to the posterior two-thirds of the interhemi- spheral cleft. It also crosses on to the caudal surface of the hemisphere and approaches, though it usually does not join, the upper extremity of the vertical calcarine This arrangement, which does not occur in the Carnivora, is of considerable interest in view of the relationship which exists between the calcarine and intraparietal (the probable representative of the lateral) sulcus and the newer inter- calated parieto-occipital sulcus in certain of the Primates {vide infra)- The antei'ior extremity of the lateral sulcus (fig. 88, 7) is overlapped on its lateral aspect by a short sagittal sulcus (y), which may possibly represent the coronal sulcus of the Cat's brain {vide infra) . There is no crucial sulcus. The mesial surface (compare figs. 89 and 90) [which is not exposed in this specimen] resembles that of the Two- toed Sloth in all its essential features {vide specimen D. 275). The cerebellum appears to be relatively very small. The floccular lobes are large cake-like masses flattened against the lateral aspect of the organ. Each of these lobes is com- posed of the usual three parts, flocculus and dorsal and ventral paraflocculi. In marked contrast to the condition found in the Armadillos [vide Cabassous, fig. 83], the dorsal paraflocculus is much the largest part of the floccular lobe in the Sloth. The rest of the cerebellum is small, narrow and simple. Its lateral parts are not expanded to the same extent as the corresponding parts in the Carnivores, the Anteaters, or even the Armadillos. In this respect the cere- bellum much more closely resembles that of such forms as Dorcatherium (Ungulata) and Hydrocharus (Rodentia). 0. C. 1323 H h. Elliot Smith, Trans. Linn. Soc. vol. vii. 1899, p. 296. D. 274. The brain of a Three-toed Sloth {Bradypus tridactylus) ( (J ), enclosed in the vascular pia and arachnoid membranes. In this specimen the independent intercalary sulcus can be seen on the mesial surface. The coronal and lateral sulci seem to be fused. 0. C. 1323 h a. K 1<: 11 \' 0 U S 8 Y8TE M . — V EKTEBK AT A . 217 D. 276. The bruin of ii Two-toed Sloth ( Cholcepus didactylus) . (Figs. 92 and are not drawn from this specimen.) In most of its features this brain presents a most strikino- resemblance to that of the Three-toed Sloth, But this Fig. 91. (Nat. size.) OLF.BULB. SULC.ORB SULC.COR.L SULC.SUPRAS SULC. ENT.L.-" general similarity renders more remarkable the peculiar absence of the so-called " Sylvian fissure " in this larger of the two brains of the Family of Sloths. 218 PHYSIOLOGICAL SERIES. The natifbrm eminence is much less prominent than it is in the Three-toed Sloth ; and the bending o£ the rhinul fissure is so slight that the whole fissure is approximately horizontal. These two facts are probably correlated with the peculiar absence of the so-called " Sylvian fissure " of the Three-toed Sloth. Whilst it is surprising to find this feature absent in the larger of the two brains, in which we should expect it to be better developed, it seems to empha- size the morphological instability of this so-called" Sylvian rig. 93. (Nat. size.) HIP.VE5T. CORP. CALL. OLF. BULB AREA PRECOM. OLF. TUBER. HIP. F. Fig. 94. (Nat. size.) PRIM. F. t CORP. qUAQ. TEL7\. FDR-MONR. COMM. ANT OPT TR COMM .MCLL CORP MAM \ PONS. CORP.INTER fissure," which a comprehensive survey of the Mammalia so clearly demonstrates. It also leads us to infer that what we may call the " feline type of Sylvian fissure " is a mere kink produced by mechanical factors, of which the most important is the downward extension of the caudo-ventral part of the neopallium. In Bradypus where such an extension has taken place (witness the ventral curve of the posterior rhinal fissure !), this so-called " Sylvian fissure' NERVOUS SYSTEM. — VEETEBRATA. 219 makes its appearance ; whereas in Cholcepus, in which the neopallium has not extended downwards in its caudal region (witness the horizontal posterior rhinal fissure), there is no " Sylvian fissure " even though the cerebral hemisphere is larger and therefore the greater a j^riori reason for a Sylvian fissure. The extensive and deep suprasylvian sulcus (fig. 92, S) is also much less acutely flexed than is the corresponding- feature in Bradypus. On its ventral side a short horizontal sulcus makes its appearance to compensate for the absence of the Sylvian element, thus affording further evidence of the mechanical mode of formation of the so-called " Sylvian fissure " o£ Bradypus. The presylvian or orbital sulcus (^) joins the rhinal fissure in both hemispheres ; otherwise it resembles that Brady- pus. On the left side it joins or becomes confluent with the rostral sulcus, but on the right side it terminates near the mesial edge just behind the upper extremity of the rostral, which is a small independent sulcus. There is an extensive, sagittal, lateral sulcus, which bifur- cates posteriorly. In this specimen (fig. 91) the lateral sulcus is fused with the coronal, but in that from which figure 92 was drawn these two elements were independent (7 and y) . There is also a well-defined entolateral sulcus — i. e. a compensatory sulcus developed on the mesial side of the lateral. The calcarine sulcus is peculiar in the Sloths in that it is independent of the intercalary sulcus (with which it is fused in most mammals to form the so-called " splenial " sulcus of Krueg). In this respect the Sloths agree with the true Anteaters, the Pangolins, and the Primates. This form of the calcarine sulcus is undoubtedly the primitive, ancestral type for all mammals. The calcarine sulcus is vertical and terminates near the upper margin of the hemisphere (fig. 93, a). The intercalary sulcus begins very far back between the splenium of the corpus callosum and the upper part of the calcarine sulcus. On the left side it extends horizontally forward almost as far as the rostral sulcus. On the right side its anterior extremity bends upward and notches the 220 PHYSIOLOGICAL SERIES. dorsal edge of the hemisphere in a manner curiously like the conjoint crucial and intercalary sulci of many Carni- vores, such as the Civet. [Figure 93 does not represent this specimen.] The corpus callosum (c.o.) and psalterium (p.s.) are relatively short and of a somewhat simple type (fig. 90), and the relations of the hippocampus to the commissures and to the supracallosal (v.H.) and precallosal (v.H.') vestiges of the hippocampal arc are clearly shown. The posterior quadrigeminal bodies are more prominent than the anterior pair, and the mesial (posterior) geniculate body on each side is so large as to appear hke a large caudal projection of the chief mass of the optic thalamus. It touches the cerebellum posteriorly. These features are some of the physical expressions of a highly acute sense of hearing. The cerebellum resembles that of Bradypus but is con- siderably larger (figs. 92 and 94). The large paraflocculus is seen to great advantage. Elliot Smith, Trans. Linn. Soc. vol. vii. 1899, p. 309. D. 276. The brain of a Two-toed Sloth [Choloepus didacUjlm) (fig- 92). In this brain the chief sulcus in the region where the " lateral " sulcus should be found obviously corresponds to that which in the last specimen was called " entolateral." There is, however, a coronal sulcus like that of Bradypus (D. 273), occupying the situation of the anterior part of the " lateral " sulcus of the last specimen ; and also a short caudal sulcus on the lateral side of the " entolateral " which appears to join the calcarine. This shows to how great an extent this group of sulci lacks morphological stability. They accommodate them- selves to slight mechanical differences in the process ot growth in such a way that no exact homology with appa- rently identical sulci in other groups can be said to exist. D. 277. A cast of the cranial cavity of a Two-toed Sloth (Choloepus didactylus). This shows the exact shape and size of the cerebellum, NERVOUS SYSTEM. — VERTEBEATA. 221 the cerebellar hemispheres, and especially of the olfactory bulbs. Gervais, Nouv. Arch. Mus., t, v. 1869, p. 38. D. 278. The brain of a Hoffmann's Sloth {Choloepus hofinanni). This brain closely resembles that of the ordinary Two- toed Sloth. In this specimen the anterior extremity of the supra- sylvian sulcus opens into the rhinal fissure, and a curious triangular depression is found behind the junction. This is more pronounced on the right hemisphere and presents a curious resemblance to the fossa Sylvii. There is, how- ever, no true Sylvian fissure, although on the left hemisphere the pit-like representatives of the compensatory supra- sylvian sulci open into the rhinal fissure so as to produce a spurious resemblance to it. It is instructive to note in this specimen how in the pyriform lobe the operation of factors such as produce the pseudosylvian sulcus in the neopallium of many mammals has converted the vallecula Sylvii into a sulcus like the neopallial pseudosylvian sulcus of other forms. On the left hemisphere there are two coextensive sagittal sulci, the mesial of which may represent either the " lateral " or entolateral " sulcus, and the external may be either the caudally prolonged " coronal " or the " lateral " (see account of specimen D. 276). On the right hemisphere the condition resembles that of specimen D. 276. None of these cranial sulci join the calcarine. There are well-developed post-lateral and paracalcarine sulci. Turner, Journ. Anat. & Phys., vol. xxv. 1890, p. 122. Family Megatheuiidje, D. 279. A cast of the cranial cavity of a Megatherium cuvieri. This presents an extraordinarily close resemblance to the Bear's brain, but is considerably larger. There is a deep oblique depression in the Sylvian region,''' and appearances suggest that there was a long 222 PHYSIOLOGICAL SERIES. oblique pseudosylvian sulcus, like that of the Bears, with an extensive suprasylvian arc presenting such an acute flexure as is seen only in the Arctoid Carnivores (of existin/nnecophaga jid>ala) ( ? ), in which the right hemisphere is separated (fig. 100). This brain is of great interest because the lips (and especially the anterior) of the Sylviap trigone are so poorly developed that this depressed area is wholly exposed. NERVO US SYSTEM. — VEKTISBRATA. 227 The suprasylvian element in the Sjlvio-snprasylvian complex sulcus is very slightly developed on the left side, and there is a small diagonal sulcus (S'). The Sylvian trigone shades away anteriorly on the right side, without any very definite terminal sulcus ; but on the Fig. 100. (xf.) RMIN.F./INT. j DLF. TUBER, jy^ ■ ''^ ^^Sr. left side there is a faintly-marked oblique terminal sulcus, which reaches almost as far as the lower extremity of the presylvian sulcus (/3). The prorean sulcus (/3') is again separate only on the ^•^■g^tside. O.C. 1323 K6-. Presented hj the Zoological Society. D. 284. The brain-stem, with part of the cerebral hemispheres, ot a Great Anteater {Myrmecophaga juhata). This specimen is intended to show the corpus striatum in the lateral ventricle ; the communication of the lattei- with the olfactory ventricle ; the optic tract spreading out on the optic thalami ; the taenia thalarai and mesial geni- culate body ; the corpora quadrigemina, of which the posterior pair are the more prorainefnt ; the insignificant tractus peduncularis transversus ; and the broad pons over- lapping to some extent the trapezoid bodies. D. 285. The brain of a Tamandua [Tamanduas tetradactyla) (figs. 101, 102, 103, 104, 105 & lOG). This is a smaller and correspondingly simplified copy of the Groat Antcatcr's brain. All traces of the "feline Q 2 228 rnYSIOLOGICAL SERIES. Sylvian fissure" have vanished (fig. 102), but the more stable suprasylvian sulcus remains in this specimen (figs. 101 & 102) to add further confirmation to the interpretation of the Sylvian complex of Myrmecophaga (D. 281). [Some- times, however, even the suprasylvian sulcus disappears in Tamanduas (fig. 103) ; this is especially helpful in inter- preting the Kodent brain, for it shows that an undoubted Fig. 101. (Nat. size.) Fig. 102. (Nat. size.) SULC.SUPRAS. SULC.LAT. rhin', f. lateral (or corono-lateral) sulcus may exist without the suprasylvian, which is usually the more precocious and stable feature.] The lateral sulcus is very shallow. In this specimen it is unsymmetrical and consists of two irregular fragments on each side. The cerebellum (compare fig. 103) is a simplified and .smaller copy of that of the Groat Antoater. The floccular NERVOUS SYSTEJr. — VERTEBRATA. 229 lobes, however, project freely, whereas those of the Great Anteater are sessile. The mesial surface of the cerebral hemisphere of Ta- manduas (compare fig. lOi) is instructive in showing the Fig. 103. (Nat. size.) OLF. COMM.ANT, exceedingly rudimentary character of the sulci, in spite of the fact that this brain is much larger than that of the Sloths and Armadillos, which have well-defined mesrial 230 PHYSIOLOGICAL SERIKS. sulci. The cerebral conunissures and hippocampus (figs. ]04 & 105) have now assumed characters like those of the Carnivores and Ungulates. Fig. 105. (Nat. size.) Vi". 106. (Nat. size.) The typical features of the base of the brain arc also well .shown (fig. 106). 0. C. 1323 k b. Elliot Smith, Trans. Linn. Soc. vol. vii. 1899, p. 293. D. 286. The brain of a Tamandua ( Tamanduas tetradadyla), ( ). There is no suprasylvian sulcus (compare fig. 103). The lateral sulcus is well marked and simple, as is also the pre- sylvian or orbital. There is a small shallow postlateral sulcus. O.C.1323Ka. NEEVOUS SYSTEM. — VERTEBKATA. 231 Family Manidje. D. 287. The brain of a Pangolin {Manis tricusjns), in which the two cerebral hemispheres have been separated from the brain-stem (figs. 107, 108, and 109). Fig. 107. (Nat. size.) OLF. BULB. SULC.ORB. SULC.SUPRAS. SULC. UT. Fig. 108. (Nat. size.) SULC. SUPRAS. SULC.LAT. SULC. ORB. .. OLF. BULB." ANT.RHIN.F / SULC. POST. RHIN. SYL . F. Fig. 109. (Nat. size.; SULC. INTER. SULC.CALC. This brain is exceedingly small in proportion to the size of the animal, and yet its small, short cerebral hemispheres present a series of deep sulci, which conform to the most typical mammalian pattern. In many points of detail tliis pattern resembles that of the Three-toed Sloth, while in other respects it resembles that of the Armadillos. I PHYSIOLOGICAL SERIES. There is a typical, short, vertical calcarino sulcus close behind the upper half of the hippocampal fissure. Like that of the Sloths, it does not join the intercalary sulcus. It, however, presents as an interesting peculiarity a short retro-calcariue branch, just as the homologous sulcus does in the Lemurs. There is an elongated intercalary sulcus of about twice the length of the small corpus callosum. In front it joins a short, oblique, rostral sulcus. It is a very suggestive fact that the intercalary sulcus, which is quite independent of the calcarine in the Anteaters and Sloths and in no other mammals except the Primates, should also be separated from the calcarine sulcus in the Pangolin. The Sylvian region [which unfortunately is irretrievably damaged in this specimen] presents very interesting features. In another damaged specimen [in the Museum Store Room] the posterior rhinal fissure, which is placed high up on the lateral aspect, is prolonged forward into a very deep orbital (presylviau) sulcus. Gervais and Weber have recorded further instances of a similar condition in Manis. This complex of posterior rhinal fissure and orbital sulcus resembles the arrangement seen in the Armadillos and, more distantly, the condition found in Orycteropus, Tapincs, and Moschus {vide infra). In this particular specimen (D. 287), however, the left orbital sulcus is certainly not joined to the rhinal fissure. The short anterior rhinal fissure does not reach so far back as the anterior extremity of the posterior rhinal. In this respect it resembles that of the Armadillos. A short, oblique " Sylvian fissure " springs from the posterior rhinal fissure, just where the latter joins, or appears to join, the orbital sulcus. The appearance of the "Sylvian^' and orbital elements recalls that presented in Galeopithecus. There is a typical semicircular suprasylvian sulcus present- ing an arcuate form. There is also a typical, sagittally- directed lateral sulcus. The cerebellum and the other parts of the brain are not unlike those of the Sloths, or, rather, present features itermediate between those of the Armadillos and Sloths. int NERVOUS SYSTEM, . — VERTEBRATA. 233 Consider ed as ii whole, the brain of the Pangolin may be reo-ftrded as a smaller and correspondingly-simplified copy of that of the Three-toed Sloth. This fact, in view of the marked contrast in the modes of life of the two animals, nmst be allowed considerable systematic importance*. 0. C. 1323 M. Presented by tlie Zoological Society. Max Weber, Zool. Ergebnisse, Leyden, 1892, p. 87. Tamily Orycteropodwa;. D. 288. The brain of an Aard-vark {Orijcteropus ajer), (?) (figs. 1.10, 111, 112, 113, 114, & 115). The brain is of approximately the same size and shape as that of the Great Anteater, but its features present a most striking contrast to it. Fio- no. (X i) In neither of the siDecimens [iu this collection] does the posterior rhinal fissure join the anterior rhinal, but the two fissures overlap (fig. 110) as they do in the Tapir {vide infra). Sometimes, however, the two fragments unite to form a * When my memoir on the Edentate brain was writtun, I had not examined a good specimen of the'hrain of Manis and had to rely on Weber's accoimt chiefly. I therefore saw no reason fur associating Manis with the other Edentates, so far as the structure of its brain is concerned. Now that I know the brain itself, I quite agree with the conclusion drawn by Windlo and Parsons from myological studies (P. Z. S. J 899), and believe that Manis shows undoubted aflinities to uU tlie other Edentates aud especially to Iiraclii2ms. l'liVsl(»I,()lilCAIi SKKIEfi. o-rcixt horizoiual fissure (fig. Ill), wliicli divides the lateral wall into two appro.ximately equal parts— an upper one of neopallium, and a lower composed of y>yriform lobe, tuhcr- culum olfactorium, and olfactory bulb. There is no trace of a " Sylvian fissure." Ther- is a typical orbital (presylvian) sulcus (/3) which links the cephalic prolongation of the posterior rhinal fissure to the anterior extremity of the great sagittal lateral sulcus (figs. 110, 111, & 113, 7), and from the junction the prorean sulcus extends forwards. Fig. 111. (X §.) RHIN.F, f /. PYR.L.' / ; OLF.tr. ; PYR.L. OLF. TUBER. Fig. 112. (Xf.) CER. PRiM.F. ; CORP PIN- CORP IpUAD OPT.THAL. ; i FLOC . F. .■' PARAFLCC . D MED OBL. OPT.tr;. i \ ; CORP. 3EN. ANT. CORP. GEN. POST \ PONS AREA TEGMEN. PARAFLOC.V. FLOC There is a short horizontal sulcus (8) in the situation where we should look for the suprasylvian sulcus. This peculiar insignificance of the suprasylvian as compared with the lateral sulcus, which is also seen in Tamandnas xn^A many Rodents, presents a marked contrast to the Ungulat(> condition, where just the opposite condition obtains. On the mesial wall there is a large arcuate c•(.mpl.^x (fi TUBER. FIM. The other parts of the brain (vide fig. 112) are not unlike those of MijrmecnpJwf/a, although there is no evidence of any close affinity between the two forms. PHYSIOLOGICAL SERIES. In general appearance and in the arrangeinent of the horizontal rhinal iissuro and its relation to the orbital sulcus, this brain ])roscnts some resemblance to that of an Ungulate. But the poor development of the suprasylvian sulcus is a point in which it differs markedly from the Ungulata. The cerebellum also differs most markedly from the simple, transversely-foliate, Ungulate type. There is a peculiar feature in the lower extremity of the hippocampal formation — a hippocampal tubercle, which is Fig. 115. (xf.) OLF.BUUB. •CPUS. CER. -—CORP. GEN. GANG. INTER V. FLOC.F .PARAFLOC. D. PARAFLOC.V. TRAP. MED.OBL. not exposed in either of these specimens. Such a hippo- campal tubercle " of inverted hippocampus I have seen elsewhere only in one o£ three specimens of the Manatee and in the Primates. I also insert here a drawing (made from a better speci- men) of the base of the brain, because it exhibits in such a striking manner the typical relations of the highly macros- matic brain (fig. 115). 0. C. 1323 L. Presented hy the Zoological Society. Elliot Smith, Trans. Linn. Soc. vol. vii. 1899, p. 286. N'li;HVOi;s SYSTRM. — VKRTKBRATA. 237 D. 289. The brain of an Aard-V^ark {Orycteropus afer), ( ? ). This specimen resembles the preceding in most respects. The suprasylvian sulcus is very insignificant. The lateral sulcus is broken up into two fragments, the anterior (coronal ?) of which does not join the orbital. O.C. 1323 La. Order CARNIVOEA. Section iELUROIDEA. Tamily Felid^. D. 290. The brain of a Domestic Cat {Felis domestica), divided by a mesial sagittal section and the right hemisphere separated from its half of the brain-stem. The Cats exhibit in perhaps their most pronounced form the peculiarities distinctive of the true Carnivores, of which they form one of the most specialised types. In the Carnivora the brain attains to much larger dimensions ni proportion to the size of the animal than is the case in the E,odentia, Edentata, and Insectivora, and this increase in size is to be attributed almost entirely to the larger growth of the neopallium. Among the secondary expressions of these larger dimen- sions of the neopallium the most noteworthy are: — A tendency of the dorso-caudal regions of the hemisphere to bulge over the cerebellum, so that the posterior margin of the hemisphere exhibits an increasing degree of obliquity : the hemisphere also grows forward so as to bulge over the olfactory bulb, and an olfactory sulcus developes on the ventral surface of this neopallium to lodge the bulb and its peduncle: and the arrangement of the sulci becomes more stable and, as it w ere, fixed. (Compare figs. 116-121, representing the Lion's brain.) The brain is still macrosmatic ; but the greater size of the neopnllium renders the greatness of the parts of the brain chiefly concerned with olfactory functions less obtrusive than is the case in mammals with a smaller neopallium. PHYSIOLOGICAL SKRIRS. Hence we find in the case of: the Cat's brain that tlie rhinal fissure (which is the line of demarcation upon the lateral aspect between the essentially olfactory pyriform lobe and the neopallium) is placed very low down on the lateral and partly on the basal surfaces of the hemisphere. [See the diiigram of the Lion's brain, fig, 116.] A short sulcus, generally known as the " Sylvian fissure," springs from the junction of the anterior and posterior rhinal fissures. This " fissure " does not correspond to that called "Sylvian" in the Benrs, and it has moreover a significance very different to the Human Sylvian fissure. Fig. 116 SULC. SUPRAS. SULC. ANS. SULC.CR SULC. COR. SULC.PROR QLF.'BULB. •' RHIN.F. ! '. sULt.DlAG ^ \ sulc.'ectos.p. VIH. SULC.ECTOS.A. ,.^ix.x.xr. \ PARAFLOC.O. 'PARAFLDC.V FLOC. Hence it will conduce to accuracy and clearness if we call it the " Feline Sylvian fissure." It may be compared to that already noticed in the brain of the Three-toed Sloth. In the left hemisphere the anterior lip of this fissure has been cut away, but there is no distinct area of cortex sub- merged in the fissure such as Holl describes (Arch. f. Anat. u. Entwick. 1899, p. 229). At the same time it will be noticed that the lower part of the fissure cuts into the hemisphere very obliquely, so that the anterior Hp overlaps the posterior lip. In the larger Felidoe this becomes much more accentuated, so that a relatively large area of the i.osterior lip becomes overlapped by the anterior hp. In -uch forms, and sometimes also in the Cat, a short sulcus NERVOUS SYSTEM. — VERTEBRATA. 239 indents this submerged posterior lip and separates it from the general surface of the hemis[)here, so that a much more definite submerged area is thus marked off. The long, deep orbital (or presylvian) sulcus is placed far forward : it opens into the rhinal fissure, and it resembles that of the Sloths. It is a characteristic of the Cats to have two vertical ectosylvian sulci — anterior and posterior — which do not unite above to form an arc as they do in the Dogs : thus a broad cortical bridge, which Meynert has called the " gyrus felinus," joins the first and second arcuate gyri of Leuret. There is a deep suprasylvian sulcus which is almost horizontal ; it becomes continuous with the vertical post- sylvian (or posterior suprasylvian) sulcus of Owen. The latter extends vertically downward to a point on the caudal margin of the hemisphere at the junction of its middle and lower thirds. The "lateral" sulcus pursues a sagittal course midway between the suprasylvian sulcus and the mesial edge. In front it bends outward parallel to the suprasylvian and gives off an " ansate " branch. The " post-lateral " sulcus begins anteriorly opposite the junction of the suprasylvian and postsylvian sulci, and pursues an arcuate course parallel to the medio-caudal " angle " of the hemisphere. On the right hemisphere it is joined to the lateral, but is separate on the left side. There is a large transverse crucial sulcus placed very far forward on the anterior pole of the hemisphere, immediately behind the mesial extremity o£ the orbital sulcus. It crosses the mesial edge and proceeds horizontally back- ward on the mesial surface for a short distance above the genu o£ the corpus callosum. There is a short oblique coronal sulcus midway between the ends of the suprasylvian and crucial sulci. Its upper (posterior) end is opposite the angle between the lateral and ansate sulci, and its lower (anterior) end is close to the orbital. In front of the ventral extremity of the anterior ectosylvian sulcus there is a short oblique diagonal sulcus." It is not uncommon to find the latter joined to the former sulcus. In other cases the diagonal sulcus may be absent. 240 PHYSIOLOGICAL SERIES. On the mesial surface of the right hemisphere, note the olfactory peduncle passing into continuity with the pre- commissural area, the upi)er part of which fills up the gap between the corpus callosum and the psalterinm, and is commonly known as a folium of the septum lucidum. Underneath the splenium of the corpus callosum the subsplenial hippocampal flexure is visible, the pyriform upper part being formed by the fascia dentata rapidly dwindling away as it surrounds the splenium : below the tapering fascia dentata there is a little tubercle of exposed hippocampus — the hijyj^ocampus nudus (the so - called " Balkenwindung ") . Behind the lower half of the typical hippocampal forma- tion the caudal part of the rhinal fissure is seen. It ends in a bifid manner. The calcarine sulcus begins above the latter, ascends vertically, and is then prolonged forward and with a slight obliquity upward, so as to overlap, without joining, the crucial sulcus : in other words, the calcarine is continuous with the intercalary sulcus. It is a feature of contrast between the ^luroidea and the Cynoidea that in the former the crucial sulcus and the intercalary (so-called "spleniar') sulcus are usually separate, whereas they commonly join in the latter. There is a short marginal sulcus (Owen) above the intercalary in the region of the splenium. On the mesial surface of the brain, note the cavity of the third ventricle bridged by the large " soft " or middle commissure : its anterior wall formed by the delicate lamina terminalis, which proceeds from the optic chiasma to the anterior commissure and then from the latter to the ventral extremity o£ the psalterium; behind the latter, the upper extremity of the lamina terminalis is seen as a little gelatinous-like nodule, the crista, to which the epithelial roof of the ventricle is attached. (The epithelial roof has been removed from the specimen.*) * The general relations of all the structures enumerated in this and the following four paragraphs do not change to any great extent in the Eutheria. Hence the reader may consult a text-book of Human Anatomy for a fuller account of them. NEEVOUS SYSTBM.—VERTEBRATA. 241 Note the pear-shaped ganglion habenulte and the taenia thalami ; the habenular commissure, the pineal bodj^, and the posterior commissure forming the upper hp of the opening of the aqueduct of Sylvius. The latter is a large canal, which expands posteriorly into a trumpet-shape. The most noteworthy features upon the lateral aspect of the mid-brain are the huge size of the mesial (posterior) geniculate body and the prominence of the posterior quadri- geminal bodies. Both phenomena are probably related to the acuteness of hearing in Cats. There is an extremely well-defined tractus peduncularis transversus. The pons, anterior pyramids, and trapezoid bodies are exceedingly clearly defined, and a slight oHvary eminence now makes its appearance at the lateral border of the pyramid. All the cranial nerves are well-developed and present the typical relations. The cerebellum presents features closely resembling the corresponding organ in the larger Edentates and in some of the Rodents. There is a large floccular lobe closely applied to the lateral aspect of the middle (or pontine) peduncle of the cerebellum and the tuberculum acusticum. The latter is easily recognised by the insertion of the auditory nerve The floccular lobe consists of three parts, viz. :— A flattened body, the flocculus {sensu stricto), closely applied to the surface of the acoustic tubercle ; a horizontal multifoliate band, the ventral paraflocculus, immediately external to this; and the dorsal paraflocculus, also a horizontal vermi- form band continuous anteriorly with the ventral para- flocculus and posterioriy prolonged into continuity with the pyramid (a part of the general mass of the cerebellum). The floccular lobes are separated from the general mass of the cerebellum by deep floccular fissures. [A similar floccular lobe may be seen to better advantage in Myrvie- cophacja (specimen D. 282) : the fundamental plan is ex- plamed by a series of diagrams in the account of Cahassous (specimen D. 268).] The interfloccular mass of the cerebellum may be sub- divided for descriptive purposes into three main parts or azygos lobes. VOL. II. ^ PHYSIOLOGICAL SERIES. The whole of the anterior surface of this mass is separated from the rest of the cerebellum by means of the deepest fissure which crosses the middle lino. This we may dis- tinguish as the anterior lobe, and its limiting fissure may be called " primary," as it is the fi.rst fissure to cross the middle line in the course of development. It corresponds to the preclival fissure of Human Anatomy. The anterior lobe represents the lobns centralis and lobus culminis of Human Anatomy. It is a large lozenge-shaped area, broad in the mesial plane and rapidly tapering towards the middle peduncle and the front of the paraflocculus on each side. The most caudal or rather caudo-ventral part of the cerebellum consists o£ a small mesial mass, the grey matter of which is not continued laterally, as that of the rest of the mesial cerebellar areas is. This may be distinguished as the posterior lobe and its dorsal limiting fissure as " secondary." The lobe represents the nodulus and uvula of Human Anatomy. Laterally it appears to be prolonged into a narrow medullary band, which is closely connected with the posterior medullary velum and leads to the flocculus. The great mass included between the primary and secondary fissures and limited laterally by the floccular fissures may be called the " central " or preferably (to avoid confusion with the " central lobe " of Human Anatomy) the " middle lobe." ,11. The middle lobe is divisible into four parts, the behaviour of the lateral parts of each of which differs markedly from that of the others. , , 1 • i The anterior lobule consists of a narrow band, which becomes slightly constricted on each side of the middle hue and then expands again to a slight extent to form a ong taperincr fissured band, which forms the posterior hp of the primary fissure. In Man this becomes greatly expanded to form the lobus clivi. The second lobule is narrow in the mesial plane, but expands enormously to form the great suprafloccular (z. above; the paraflocculus) mass, the folia of which are arranged in a feather-like pattern in all the Carnivora. It presents a similar arrangement in the Anteaters, the NBRVOaS SYSTEM. — VBRTBBRATA. 243 Aard-vark, and many Rodents, but in many Ungulates and Rodents there is no such lateral expansion in a feather-like pattern, but a simple transverse arrangement of the folia. In the Primates this region of the cerebellum becomes so enormously expanded that it forms the great mass of the organ. The third lobule consists of an extremely narrow mesial bridge connecting two large vertical worm-like masses, which extend downward on the caudal surface and separate the posterior lobe from the paraflocculus. The fourth lobule consists of the pyramid, which is laterally joined to the dorsal paraflocculus by a narrow band, which has become so compressed by the downward growth of the third lobule as to be ]-ecognised with difficulty in the Cat's brain. It is, however, clearly shown in such brains as that of Lepus and Cabassous. Burt G. Wilder, Proc. Amer. Phil. Soc. 1881, p. 524. D. 291. The brain of a Cat {Felis domestica), in which the corpus callosum has been cut through in a sagittal direction and the cerebral hemispheres widely divaricated. The caudate nuclei lying in the lateral ventricles have been thus exposed. The optic thalami have been drawn asunder and the soft commissure partially torn through, so that the slit-like third ventricle has been converted into a widely open space the limits of which are indicated by the taenise thalami, which together form a semicircle. The corpora quadrigemina are exposed, and external to the anterior quadrigeminal body the large mesial geniculate body may be seen immediately behind the optic thalamus. ITiis mesial geniculate body may also be well seen upon the left side of the base of the brain, the natiform portion of the pyriform lobe having been removed in order to 0. C. 1325 D. D.292. The brain of a Cat [Felis domestica) presenting an anomalous arrangement of the cerebral sulci. On the right hemisphere the pseudosylvian sulcus is very short, and on the left is reduced to a mere notch in R 2 244 PHYSIOLOGICAL SERIES. the upper lip of the rhinal fissure. This arrangement is similar to that presented by the brain of Jlerj^estes. The ectosylvian sulci are very deej), as if to compensate for the diminutive size of the pseudosylvian. The anterior and posterior ectosylvian sulci appear to be joined into an arc on both sides as in Cynoidea ; but they are in reality separated by a feline gyrus which is partly submerged. There are a series of fragmentary sulci between the posterior ectosylvian and the postsylvian. The postlateral is a short branch of the latter sulcus, and is quite independent of the lateral sulcus. The latter is continuous on the left side with a long and tortuous coronal sulcus. There are well- marked but shallow representatives of an entolateral sulcus on each hemisphere. This specimen is of special interest as a further demon- stration of the fact, which has already been noted in the Sloths and the lowlier Mammalian Orders generally, that the " Sylvian fissure " (so-called) is at first a very unstable feature and only becomes definitely " fixed " in the higher Mammalia. It further illustrates the reciprocally com- pensatory development of the pseudosylvian and the ecto- sylvian sulci, of which we meet many instances elsewhere*. D.293. The brain of a new born Lion {Felis leo). The only noteworthy features in this specimen are a series of peculiar notchiugs in the upper lip of the rhinal fissure in front of the pseudosylvian sulcus, and the extreme irregularity of the latter and of the ectosylvian sulci. 0. C. 1325Aa. D.294. The brain of a Lioness {Felis leo), in which a dissection has been made to show the hippocampus in the left hemi- sphere. The brain of the Lion when compared with that of the Cat affords an admirable demonstration of the influence of * In the accentuation of the ecto- at the expense of the pseudosylvian sulcus this anomalous brain resembles the Ungulate type, the so-called " Sylvian fissui-e " of which is formed by the meeting of the lips of the two ectosylvian sulci. In this case also the feline pseudosylvian sulcus becomes greatly reduced or even disappears. NERVOUSl SYSTEM. — VERTEBRATA. 245 the size of the body upon the proportions and form of the brain. In animals of the same Order (and more especially of the same genus) the brain is much larger in the bigger species ; but the increase in size is not proportionate to that of the bodily dimensions, the smaller animal having a brain relatively much larger than that of the bigger animal. This is due to the fact that in mammals of the same genus (i. e. in animals in which the other determining factors of the size of the brain may be neglected as being common to the two forms) the size of the pallium varies directly with that of the areas of the sensory surfaces, and these are relatively greater in a small than in a large animal. (See Dubois, Bull. d'Anthropol. de Paris, 1897, p. 337.) As a result of the larger size of the neopallium, the sulci become deeper and longer and secondary sulci make their appearance. FiR. 117. * The " Sylvian fissure " (so-called) is much deeper and cuts into the neopallium much more obliquely than is the case in the Cat's brain. Thus a large anterior lip is de- veloped so as to overlap the depressed posterior lip, which is exposed by raising, or better by cutting away (fig. 117), the anterior Hp. The submerged posterior lip is then seen to be indented by two sulci (fig. 117, a and b). In this specimen (D. 294) the condition thus described as typical of the Lion's brain does not obtain, and a condition essen- tially identical with that of the Jaguar's brain {vide infra D. 297) is present. * [The following remarks are based upon the careful examination of the brains of three Lions, which were removed from the skulls by the writer shortly after the death of the animals : thus a more accurate account is given than would be pobsiblu from the study of old Museum specimens.] PHYSIOLOGICAL SEUIES. In front of the " S)>lvian fissure " ;i short, deep, vertical sulcus extends upward from the rhinal fissure (figs. 116 & 117, x). The anterior ectosylvian sulcus (fig. IIG) is very deep, and its lips are puckered so as to ])roduce short secondary sulci in some cases. In all of the eight hemispheres i have examined it is confluent with a very deep, long, horizontal " diagonal sulcus," which also in most cases gives off short secondary branches. In some cases (fig. 118) the anterior limb of the first arcuate gyrus of Leuret becomes submerged in the " Sylviari fissure," so that the anterior ectosylvian sulcus becomes hidden in the latter and the diagonal sulcus appears (at a casual glance) to emerge from the Sylvian fissure itself. Fig. 118. (x|.) SULC.ECTOS.P. RHIN.F. "" Such a phenomenon is of great interest as an indication of the very general tendency (among the Mammalia generally) for the cortical areas in front of the "feline Sylvian'' fissure to become engulfed in it. In the Bears, not only the anterior limb but the whole of the first arcuate gyrus becomes swallowed up in the " Sylvian fissure." It is unnecessary to describe in detail the effects of the deepening and development of secondary branches in the case of the posterior ectosylvian, suprasylviau, and corono- lateral group of sulci. These are obvious at a glance ffig. 116). It is of interest to note that the exceedmgly deep orbitjil (presylvian) sulcus is independent of the rhinal fissure ; a fact which is veiled in the Cat by the upper operculum of the sulcus meeting the pyriform lobe. NEllVOUS SYSTEM. — VERTEBllATA. 247 It is a very interesting fact that an undoubted precrucial sulcus is found in the deep crucial sulcus. Sometimes this sulcus is exposed (fig. 119) ; in other cases it is hidden by the opercular posterior lip of the crucial sulcus and is visible only after raising or removing this (fig. 120) . So that in Fij?. 119. (xf.) Fig. 120. ( X f.) Fig. 121. (x§.) SULC.CRU. SULC, INTER. RHIN.r. this Feline brain we find a very distinct " Ursine lozenu-e " of Mivart. Another feature of great interest in the Lion's brain is exposed on separating the lips of the deep " splenial " 248 PHYSIOLOGICAL SERIES. complex, when it is seen that the calcarinc sulcus is really distinct from the intercalary in this Carnivore, as it is in the Edentata and Primates (fig. 121). 0. C. 1325 a. Krueg, Zeitsch. f. wiss. Zool., Bd. xxxiii. 1880, p. 617. D. 295. . The brain of a Tiger {Felis tigris). In a comparison of the brain of the Tiger with that of the Cat, we observe a series of changes analogous to those which are found in the Lion's brain when contrasted with the latter. The arrangement of the Sylvian region re- sembles that described as typical of the Lion (D. 292). 0. C. 1324. Hunterian. D. 296. A cast of the cranial cavity of a Tiger {Felis tigris). This shows the true proportions of the large flattened olfactory bulbs which are placed well in front of the hemispheres. D. 297. The brain of a Jaguar [Felis onca). Note the continuity of the anterior ectosylvian and the long diagonal sulcus ; also the apparent connection of the former with the upper part of the pseudosylvian sulcus, as in the Lion's brain (fig. 118): and the numerous secondary sulci springing from the convexity of the suprasylvian arc. 0. C. 1325 B. D. 298. The brain of a Leopard {Felis pardus) . Note that the upturned cephalic extremity of the inter- calary sulcus (the non-calcarine part of Krueg's splenial sulcus) crosses the dorso-mesial edge of the hemisphere so as to simulate the crucial sulcus. The true crucial sulcus is placed further forward and is completely separated from the intercalary sulcus, as is usual in the Felidae, Note the well-developed marginal sulcus of Owen (the conjoint supra- and post-splenial of many writers). The anterior ectosylvian sulcus is continuous with the diagonal, and on the left hemisphere joins the posterior ectosjdvian to form a complete ectosylvian arc as in the Cynoidea. 0. C. 1325 n a. Krueg, Zeitsch. f. wis^. Zool., Bd. xxxiii. 1880, j). 617. NERVOUS SYSTEM. — VEUTEBRATA. 249 D. 299. The brain of an Ocelot (Fdis i^ardalh) . A typical simple Feline brain. 0. C. 1325 B b. D. 300. The brain of a Cheetah (Cyncelurus jubatus) . Note the exceptionally well-developed pseudo-crucial sulcus behind the ansate. It is merely the upturned anterior extremity of the intercalary sulcus. The right suprasylvian sulcus is not joined to the postsylvian. \ As also in the Ocelot, the diagonal is an independent sulcus. 0. C. 1325 c. Holl, His's Archiv, 1899, p. 230. I'amilv VivERRWJii. D. 301. The brain of an African Civet {Viverra civetta), ( ? ), (figs. 122, 123, and 124). Fzrr. 122. (Nat. size.) The features ot the brain in this family are especially interesting because the instability of the " Sylvian fissure^' (so-called) and the crucial sulcus are so strikingly demon- strated. In regard to these peculiaritie.'^, the brain of the PHYSIOLOGICAL SERIES. Civet and its near relations may be regarded as connecting links between the typical Carnivora and the lowlier mam- malian orders in which the crucial sulcus is absent and the " Sylvian fissure " imperfect or wanting. The orbital (prcsylvian), corono-lateral, and suprasylvian sulci are simple and quite typical (figs. 122 & 123)." The suprasylvian sulcus is the deepest sulcus in the hemisphere. Fig. 123. (Nat. size.) SULC. CDR.LAT; sulc.supras. / ""v SYL.ECTOS. COMP. Fig. li>4. (Nat. size.) SULC. INTER. SULC.CALC. A very deep calcarine is prolonged forward into the intercalary sulcus which in turn joins the crucial sulcus (fig. 124). The latter is so small (fig. 122), that it barely reaches the dorsal surface. The genual sulcus is joined to the crucial sulcus on the left hemisphere by a shallow furrow (fig. 124). The " feline Sylvian fissure " is so ill-defined that there is a conflict of opinion as to which sulcus really represents it. This further exemplifies the morphological instability NEliVOUS SYSTEM. — VERTEBKATA. 251 of this sulcus, which has already been noted iu the Cats, Sloths, and other forms. According to Hell the representative o£ the Sylvian fissure is found in a small notch above the bend in the rhinal fissure. But there can ■ be little doubt that this really represents what Holl himself would call the " anterior ter- minal sulcus of the trigonum Sylvii." It is continuous, under the pallial operculum, with the orbital (presylvian) sulcus. On the right hemisphere this notch is so insignifi- cant that it might easily pass unnoticed (fig. 123, x). The sulcus which at a casual glance would be unquestion- ably called Sylvian fissure " in this hemisphere is fairly deep and extensive, and opens freely into the rhinal fissure behind the before-mentioned notch or " Sylvian fissure'' (according to Holl). Holl regards this sulcus as the posterior ectosylvian : and there can be no doubt that it does represent the posterior ectosylvian ; but it is some- thing more — a confluence of the latter and the sulcus which Holl calls " posterior terminal." In the case of an anomalous Cat's brain {vide specimen D. 292) it was seen that the ectosylvian sulcus and the " feline Sylvian fissure " might be compensatory factors in relieving the tension of pallial expansion in this region ; we know also that it is not uncommon for the posterior ectosylvian sulcus to open into the Sylvian fissure or to join HoU's " posterior terminal sulcus " ; it is also known to be unusual for the ectosylvian sulcus to join the rhinal fissure, whereas it is the usual arrangement of the Sylvian fissure : these facts and, finally, a comparison with other Viverridas and with Carnivores of other families (see especially Holl's figures of the brain of a Cheetah [Taf. xi. fig. 2] and of a Fox's brain [Taf. xi. fig. 12]) show that this posterior sulcus (fig. 123) in the Civet ought to be regarded as the representative not only of the posterior ectosylvian sulcus, but also of the " feline Sylvian " fissure *. * If wo compare tliia brain with that of the Jaguar (D. 297), we can greatly simplify matters by calling the sulcus labelled " syl. ectos. COMP." (fig. 123) simply " pseudosylvian," and the sulcus x the repre- sentative of that similarly labelled in figs. 116 and 117. 252 PHYSIOLOGICAL ISIiUIES. The object of this lengthy digression is not so much to interpret the individual condition here present — a question of small moment — but to emphasise the variability and morphological instability of the " feline Sylvian fissure " and its compensatory ectosylvian sulci. It is only when the " feline Sylvian " becomes blended Avith the stiible suprasylvian sulcus, as in Myrmecopliaya and the Primates, that the real " Sylvian fissure " can be said to exist in a really stable condition. An irregular horizontal sulcus extends forward from the upper end of the ectosylvian in this specimen and, together with the several pit-like markings, represents the anterior ectosylvian sulcus. [Compare the condition in Felis onca, D. 297.] Otherwise this specimen affords an admirable demon- stration of the typical features of the Carnivore brain. Note the prominent tubercle of the olfactory tract in the vallecula Sylvii (the depression between the tuberculum olfactorium and the natiform, caudal part of the pyriform lobe) : the well-defined tractus peduncularis transversus of Guddeu (Wilder's cimbia) on the lateral aspect of the crus cerebri: the large auditory nerve inserted into a very prominent and bulky acoustic tubercle, from which a large trapezium extends as far as the lateral edge of the exceptionally prominent pyramidal tract. The features of the cerebellum, which is a simplified form of that of the Cat, are shown exceeding clearly. 0. C. 1325 1 a. Holl, Arch. f. Anat. u. Entwick. 1899, p. 243. D. 302. The brain of an African Civet {Viveii'a civetta). This specimen even more decisively than the last supports the contention that the larger, deeper and more posterior of the two sulci opening into the bend of the rhinal fissure represents not only the posterior ectosylvian sulcus but also the " feline Sylvian fissure.'^ A comparison with the brain of the Mongoose {virle infra) shows this conclusively. It certainly caiinot be regarded as the posterior ectosylvian only. The lower extremity of the latter can, in iiict, be NERVOUS SYSTEM. — VERTEBRATA. 253 seen indenting the posterior lip of the sulcus at about its mid-point. The posterior ectosylvian sulcus gives off no branches such as its representative in the other specimen exhibits. The sulcus which Holl {op. cit.) would call the " anterior terminal (i. e. the anterior limit of the area usually sub- merged in the " Sylvian fissure ") is much longer in this specimen, especially on the right side. 0. G. 1325 I. D. 303. The brain of a Genet (Genetta vulgaris). The brain of the Genet closely resembles that of the Civet as I'egards most of its features. There is no typical crucial sulcus. There is, however, a shallow depression on the dorsal surface, which is regarded by some writers as the representative of the crucial. On the right side the intercalary sulcus extends obliquely forward and upward almost as far as the doi'sal edge far forward in the hemisphere. On the left side the true intercalary sulcus is quite dis- tinct from an anterior sulcus which may possibly represent the crucial. No ectosylvian sulcus can be recognised with any degree of certainty, but there is a pseudosylvian sulcus resembling that of the Cat. 0. 0. 1325 H b. D. 304. The brain of a Genet {Genetta vulgaris). 0. C. 1325 H. D. 305. The brain of an African Genet [Genetta tigrina), ( ? ). This resembles that of the Common Genet. 0. C. 1325 Ha. Presented hy St. George Mivart, Esq. D. 306. The brain of a Cape Mongoose [Herpestes pulveru- lentus), [S)- This brain is peculiar in many respects. There is a very extensive crucial sulcus placed far forward on the hemisphere and in free communication with the intercalary sulcus on the right side, but not on the left. This is all the more noteworthy when the slight development or absence of a crucial sulcus in other Viverrida3 is recalled. 254 PHYSIOLOGICAL SERIES. The orbital sulcus is very small, and placed so far forward on the apex of the hemisphere that it is hidden bv tlie olfactory bulb, and is believed by many writers {e. g., Ziehen, Arch. f. Psych. 1896) to be absent. The deepest sulcus on the hemisphere is the suprasylvian which extends backward above, but without joining the vertical postsylvian (compare fig. 125). Holl {pp. c.ii. p. 238) considers that no Sylvian fissure is present, but we can have little hesitation in regarding the sulcus which springs from the junction of the deep anterior rhinal and the shallow post-rhinal fiissures as the pseudo- sylvian sulcus. After a short oblique course upward and slightly backward, it joins the posterior ectosylvian which Fig. 125. (Nat. size.) SULCSUPRAS. SULC.ENT.LAT. SULC. CRU. • SULC.LAT. / i ; i / OLF.BULB. -^X^Z^--^-^^^^^^^::^^^^^^ SULC.P.SYU SULC.ECTOS.P. pursues a short course upward and forward and is then joined to the anterior ectosylvian sulcus (compare Holl's fio-ure of Herpestes ichneumon). lateral sulcus is apparently fused to an ansate element in front, but is not joined to the small oblique coronal sulcus. The shallow postlateral is prolonged forward as a fragmentary entolateral sulcus. 0. C. 132» I c. Holl, Arch. f. Anat. u. Entwick. 1899, p. 238. Mivart, Journ. Linn. Soc, vol. xix. 1886, p. 7. [Since this account was written I have examined the brains of two specimens of Herpestes ichneumon, and the interesting variations in these four hemispheres decisively show that the real nature of the sulci in question accords wiih the suggestions in the accounts already given. NERVOUS SYSTEM. — VBRTEBRATA. 255 On the loft hemisphere of the first specimen (fig. 125), the " Sylvian fissm'e " is an extremely short notch in the tipper lip of the rhinal fissure and the posterior ectosylvian sulcus (which is independent of the anterior ectosylvian) ends in very close proximity to this small pseudosylvian. On the right hemisphere the pseudosylvian is larger and surrounded by a distinct ectosylvian arc (fig. 126). In the left hemisphere of the second brain (fig. 127) there are two " Sylvian notches," o£ which the longer overlaps the posterior ectosylvian so that Fig. 126. Fig 127. at a casual glance they might easily be mistaken for one fissure. On the right hemisphere (fig. 128) a similar arrangement of the only "Sylvian element''' is found. Figure 129 represents yet another variety. These specimens clearly show the real nature of the pseudosylvian sulcus, or " Sylvian fissure " so-called, in the Viverridse.] D. 307. The brain of an -iEvisa {Crossarchus obscurus), ( ? ). This may be regarded as a simplified Herpestine brain. The " Sylvian fissure " seems to be absent in this specimen. 0. G. 1325 iZ*. D. 308. The brain of a Palm-Civet {Paradoxurus typus) , ( ? ) . There is a typical " feline Sylvian fissure " : orbital and posterior ectosylvian sulci as in the Felida3 and Hysenidse ; a typical suprasylvian sulcus forming a regular arc with the postsylvian ; conjoint coronal and lateral sulci without any ansate ; and no true crucial sulcus. There are, how- ever, some shallow pits, where the crucial sulcus occurs in other brains, and the coronal sulcus has an unusual 250 PHYSIOLOGICAL SERIES. inclination forward and inward. The intercalary sulcus (the cephalic extension of the calcarino — the " splenial " of Krueg) extends almost to the cephalic pole of the hemi- sphere. There is a short genual sulcus. 0. C. 1325 G c. Krueg, Zeitsch. f. wiss. Zool., Bd. xxxiii. 1880, p. 628. D. 309. The brain of a Palm-Oivet {Paradoxurus typus). An ansate sulcus is present in this specimen, and in front of it thei'e is a definite furrow which may represent the crucial sulcus. 0. C. 1325 6 d. D. 310. The brain of Hemigale Jiardivickii. This brain resembles that of Paradoxurus. Note, however, the upturning of the anterior end of the intercalary (or splenial) sulcus, which may represent the otherwise missing crucial sulcus. (This, however, hardly accords with the suggestion made concerning the representative of the crucial sulcus in Paradoxurus.) 0. C. 1325 H c. D. 311. The brain of a Binturong {Arctictis binturong). In most respects this brain resembles those of Para- doxurus and Hemigale. There appear, however, to be two " Sylvian-like " sulci opening into the angle of the rhinal fissure. They may be regarded as the two " terminal sulci " of Holl, the posterior of which is concurrent with the posterior ectosylvian sulcus. In many Carnivores there is a small submerged area in the Sylvian fissure called the "trigonum Sylvii " by Holl. The bounding fissures of this trigone he calls the terminal sulci : in this specimen they are exposed on the surface so that there is no true " feline Sylvian fissure." On the right hemisphere there is a faintly-marked crucial sulcus quite independent of the forward prolongation of the so-called " splenial " sulcus. It is more indistinct on the left side. There is a broad gyrus between the corono-lateral sulcus and the mesial plane, indented by numerous short sulci on the right hemisphere and by pit- like short sulci on the left side. The ansate is represented by a pecuUar arc-like sulcus quite independent of the lateral. . O.C.1325Fa. Mivart, Journ. Linn. Soc, vol. xix. 1886, p. 7. NEKVOUS SYSTEM. — VERTEBRATA. 257 D. 312. The brain of the Suricate (Suricata tetradactyla) , {^). In most respects this brain closely resembles that of Ilerpestes. The " Sylvian fissure " is a mere notch in the upper lip of the rhinal fissure, surrounded by an arcuate ectosylviau sulcus : there is a large crucial sulcus and a small orbital (presylvian) sulcus, which, under normal conditions, would be completely hidden by the olfactory bulb. 0. C. 1325 G. Mivart, Journ. Linn. Soc, vol. xix. 1886, p. 8. Presented hy J. Lemage, Esq. D. 313. The brain of Nandinia hinotata. This resembles the brain of the Genet in most of its features. The Sylvian region, however, resembles that of the Civet's brain, more especially as seen in specimen D. 302. 0. C. 1325Ga. Mivart, Journ. Linn. Soc, vol. xix. 1886, p. 6. D. 314. The brain of Nandinia binotata. ^ Note the absence of the crucial sulcus and the insig- nificant proportions of the mere notch which represents the " Sylvian fissure.^' 0. C. 1325 G h. Family HyjeniDje. D. 315. The brain of a Hya-na {Hyc&na hycona), (cj).' The so-called "Sylvian fissure^' (fig. 130) presents a marked contrast to the similarly-named feature of the Fig. 130. (x§.) SULC.COR. SULC.SUPRAS. Cat's brain ; in the latter it is short and relatively shallow, whereas it is very long and deep in the Hysona. At a VOL. n. a PHYSIOLOGICAL SERIES. casual glance the anterior ectosylvian sulcus is absent, and this at once reminds us of the spurious or apparent lengthening of the " Sylvian fissure " in the Lion (vide supra), where the anterior ectosylvian sulcus becomes engulfed in the "Sylvian" (fig. 118). If the prominent opercula-like lips of the " Sylvian fissure " in the Hyana be separated it vfill be found that the upper half of the fissure is really a submerged ectosylvian ; in some cases {vide fig. 131), but not in this, the lower extremity of this ectosylvian element emerges from the " Sylvian " and deeply incises its anterior lip. But the condition in the Hyaena's brain is very different even from that of what we may call the anomalous Lion's brain (fig. 118). There is a very large triangular submerged area (which Fig. 131. (Nat. size.) Fig. 132. (Nat. size.) HoU would call " trigonum Sylvii ") overlapped not only by a large anterior operculum but also by a still larger posterior operculum. This "trigone" is limited both in front and behind by well-defined limiting sulci. The inferior extremity of the posterior limiting sulcus may emerge from the " Sylvian " cleft a short distance above the rhinal fissure (fig. 131, c, also specimen D. 319). In the middle of the trigone there is a deep sulcus Hke the feline " Sylvian fissure " (fig. 132, a). But a careful study of the conditions existing here clearly shows that neither the superficial pattern formed by the meeting of the opercular lips nor this submerged sulcus can be regarded as strictly homologous to the " feHne Sylvian fissure." The whole arrangement is a more or less direct mechanical adaptation of the growing cortex in this region of kinking, and varies in different fomilies of the Carmvora NERVOUS SYSTEM. — VEKTEBRATA. 259 just as it frequently does even in members of the same genus and species. There is a deep, simple, posterior ectosylvian sulcus, which is quite separate from the anterior sulcus, as in the Cats (fig. 130). There is a great suprasylvian arc formed usually of conjoint diagonal, suprasylvian and postsylvian sulci, but Fig. 133. (x§.) SULC.COR. -SULC.LAT. SULC.SUPRAS •SULC.ECTOS.P. SULCPSYL. SULCCRU. Pig. 134. (x§.) SULC. INTER. SULC.MARG. SULC. CALC. HIP. F. sometimes the diagonal sulcus uuy be separate (figs. 130 & 133), as m the right side of specimen D 317 There are large typical coronal, lateral, and postlateral sulci and a very long deep orbital (presylvian) sulcus, with occa,sionally a small accessory orbital springing from the rhmal fissure still further forward. ^ ^ ^ s 2 260 PHYSIOLOGICAL SERIES. There is a very deep, long, transverse, crucial sulcus (fig. 133) ; and in some cases, i£ it be opened up, a small indubitable precrucial sulcus is present. The crucial sulcus is joined by the intercalary to the deep calcarine sulcus, as is commonly the case in the Dogs (fig. 134). There nre, in many Hysenas, numerous irregular accessory post- calcarine sulci — the irregular forerunners of the retro- calcarine and collateral sulci of the human brain. There is also a well-developed marginal (" suprasplenial ") sulcus. The genual sulcus in some cases proceeds upward to join the precrucial. 0. C. 1325 b a. D. 316. The brain of a Hysena (Ilycena liycena). 0. C. 1325 Be. D. 317. The brain of a Hysena [Hycena hycena), ( ? ). 0. C. 1325 EfZ. D. 318. The brain of a Hysena {Hycena hycena), ( ? ). 0. 0. 1325 eZ). D. 319. A brain labelled " Hysena." Although much larger than the other specimens of the Hysena's brain, this specimen presents similar features. The " Sylvian fissure," however, is more open and the sulcus which emerges and indents its posterior lip — perhaps the " posterior terminal sulcus " of Holl — is unusually well pronounced. 0. C. 1325 e. D. 320. A cast of the cranial cavity of a Spotted Hyaena {Hywna croeuta) . This shows the size and shape of the olfactory bulbs, which are distorted in the specimens of the brains them- selves. Note that the open condition of the pseudosylvian sulcus is natural, as it is seen in the cast. Gervais, Nouv. Arch. d. Mus., t. vi. 1870, p. 125. D. 321. The brain of a Froteles cristatus, (cJ). This closely resembles the brain of the Hyajna. It is of interest to note a retrocalcarine sulcus extending NERVOUS SYSTEM. — VERTEBRATA. 261 backward and upward from the "spleniar' complex of calcarine and intercalary sulci after the manner o£ the Fig. 135. (x|.) SULC.LAT. SULC . SUPRAS. Fig. 136. (x§.) SULC.CRU. SULC. INTER. posterior calcarine snlcns in the Primates (figs. 135, 130, &137). O.C. 1325 r. Flower, Proc. Zool. 8oc. 1801), p. 478. 262 PHYSIOLOGICAL SERIES. Section Ctnoidea. Family OanidjK. D. 322. The brain of an Otocyon {Otocyon megalotis). The anterior and posterior ectosylvian sulci meet and form a regular arc around the short Sylvian fissure. This is one distinctive feature of the Cynoidea in contrast to the iEluroidea. On the left hemisphere there is a short vertical offshoot from the ectosylvian arc. The suprasylvian and postsylvian sulci are united into a regular arc and there is no separate diagonal sulcus. The lateral and short postlateral sulci are joined on both sides, and on the left side the lateral joins the coronal. There is a well-developed orbital (presylvian) and a short transverse crucial sulcus. Midway between the postsylvian and postlateral sulci there is a short vertical " ectolateral " sulcus. This is a very characteristic feature o£ the Gynoid brain. 0. (1 1325 M. Gervais, Nouv. Arch. Mus., t. vi. 1870, p. 109. D. 333. The brain and the upper part o£ the spinal cord of a Common Fox ( Vulpes vulpes) . This specimen exhibits with diagrammatic clearness the typical Gynoid characters : — the three regular arcuate sulci (ectosylvian, suprasylvian, and corono-lateral respectively) surrounding the short oblique pseudosylvian. The cha- racteristic ectolateral sulcus, the orbital and the deeply- incised oblique crucial sulci complete the picture. There is a small ansate sulcus joined to the coronal on the left side, and an altogether insignificant separate ansate on the right side. It will be noted that such other parts of the brain as can be seen in this specimen resemble the corresponding parts in the Gat's brain. 0. G. 1325 l. Krueg, Zeitsch. f. wiss. Zool., Bd. xxxiii. 1880, p. 612. D. 324. The brain of Canis microtis, in which the left cerebral hemisphere has been separated, {S)- In this specimen we can see the continuity of the crucial NEIIVOUS SYSTEM. — VERTEBRATA. 263 and the intercalary splenial ") sulci (fig. 140) — another feature usually presented by the Dogs. In addition it also exhibits (figs. 138 & 139) the other two Cynoid characters — the complete ectosylvian arc and SULC.CRU SULC. COR Fig. 138. (Xf.) SULC.ECTOLAT. SULC. DRB S / SULC.SUPRAS. SULC ECTOSYL. Fig. 1.39. (xf.) SULC .CRU. SULC. ANS. SULC.LAT. • SULC.SUPRAS. I-SULC.ECTOLAT. Fig. 140. (x§.) SULC.INTERCAL. SULC.CRU... MARG (POST CALC.) •SULC.CALC. RHIN.F. the presence of the ectolatoral sulcus — in a typical for™- 0. C. 1325 L /. Mivart, Journ. Linn. Soc, vol. xix. 1886, p. 3. 264 PHYSIOLOGICAL SERIES, D. 326. The brain of a Bush Dog [Sjyeothos venaticus), { ? ). A complete ectosylvian arc is present only on the right side, and even there its anterior limb is short and appears to be joined to the " Sylvian fissure." On the left side the small posterior ectosylvian sulcus joins the pseudo- sylvian a short distance below the apex of the latter. A comparison of this condition with that of the Viverridaj is interesting. Fig. 141. (x§.) The postlateral sulcus is absent on the right side and represented merely by a shallow pit on the left side (fig. 141). 0.0. 1325 L