^T OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES No. 128, 78 pages, 31 figures, 1 table June 22, 1978 Cranial Nerves of a Pereoid Fish, Polycentrus schomburgkii (Family Nandidae), a Contribution to the Morphology and Classification of the Order Perciformes By Warren C. Freihofer Department of Ichthyology, California Academy of Sciences, Golden Gate Park, San Francisco. California 94118 tfJ&E/lfy SAN FRANCISCO PUBLISHED BY THE ACADEMY o COMMITTEE ON PUBLICATIONS Laurence C. Binford. Chairman Tomio Iwamoto, Editor Paul H. Arnaud. Jr. William N. Eschmeyer George E. Lindsay The California Academy of Sciences Golden Gate Park San Francisco. California 941 18 PRINTED IN THE UNITED STATES OF AMERICA BY ALLEN PRESS INC.. LAWRENCE, KANSAS Table of Contents Abstract v Introduction 1 Methods 2 Literature on Nerves of Perciform Fishes 3 Family Nandidae 3 Names of Cranial Nerves 4 Nerve Components 4 Descriptions of Nerves 5 Radix Profundus 5 Fifth and Seventh Cranial Nerve Roots, Trunks, and Rami 6 Roots and ganglia of nervus trigeminus 8 Communis root and geniculate ganglion 8 Dorsal lateralis root of facial nerve 8 Gasserian ganglion of nervus trigeminus 9 Roots and ganglion of nervus facialis 9 Ramus communicans of nervus trigeminus 10 Truncus Supraorbitalis 10 Ramus ophthalmicus superficialis trigeminus and r. ophth. supf. facialis .... 10 Truncus Infraorbitalis 13 Ramus buccalis facialis 13 Ramus ma.xillaris trigeminus 15 Ramus mandibulars trigeminus 16 Ramus operculars trigeminus 16 Innervation of cheek muscle 17 Ramulus mandibulars cutaneus trigeminus 17 Ramulus mandibulars externus trigeminus 19 Ramulus mandibulars interims trigeminus 20 Ramus Oticus 20 Ramus Palatinus 21 Truncus Hyomandibularis 22 Ramus operculars profundus facialis 23 Ramus operculars superficialis facialis 23 Ramus hyoideus 24 Ramus mandibulars facialis 25 Ramus buccalis accessorius facialis 26 Ramus mandibulars externus facialis and ramus mandibularis internus facialis 26 Ramus Lateralis Accessorius 29 The orbit o-pectoral branch (RLA-OP) 29 The parieto-dorsal branch (RLA-PD) 30 Innervation of the Gill Arches 30 Nervus Glossopharyngeus 31 Nervus Vagus 31 Intracranial dorsal vagal ramus 32 Rami cutanei dorsales vagi 33 Ramus operculars vagi 33 Ramus supratemporalis vagi 34 First vagal branchial trunk 34 Second vagal branchial trunk 35 Third vagal branchial trunk 36 Fourth vagal branchial trunk 37 Summary of Gill-Arch Muscle Innervation 37 Lateral Line Nerves of the Trunk 37 Nervus Linae Lateralis 38 Discussion 39 Free Cephalic Lateralis Organs 39 Comparison with Perca fluviatilus 39 Comparison with Menidia 40 Comparison with cyprinids 40 Comparison with esocoids 41 Comparison with Amia 41 Cephalic Lateralis Canals and Neuromasts 41 Innervation of Upper Jaw 44 Cheek Muscle Innervation 45 Correct Name for Ramus Lateralis Accessorius 45 Trunk Lateral Line Nerves 46 An External-Internal Lateral Line Canal Nerve Relationship 46 Radix Profundus 47 A Stretch Receptor Nerve to Base of Maxillary Tendon 47 Simplifying Cranial Nerve Studies 47 Summary 48 Acknowledgments 50 Literature Cited 52 Abbreviations for Figures 54 Illustrations 57 Abstract Freihofer, Warren C. Cranial nerves of a percoid fish, Polycentrus schomburgkii (family Nandidae), a contribution to the morphology and classification of the order Perciformes. Occasional Papers of the California Academy of Sciences, no. 128, 78 pages, 31 figures, 1 table, 1978. — Four cranial nerves, the trigeminus, facialis, gJossopha- ryngeus. and vagus, of Polycentrus schomburgkii (Nandidae) are described and illustrated (including muscles of jaws and gill arches) in detail from cleared-and-stained nerve preparations of whole specimens and from serial sections. The nerves are described in terms of their main functional components. The descriptions are intended as a basic reference for comparative nerve studies of perciform fishes for systematic purposes. Comparisons were made with numerous other families (85 represented as nerve preparations) for particular points such as the inner- vation of the snout, upper jaw, cephalic lateral line canals and pitorgans. cheek musculature, and trunk lateral line systems. In many features of its cranial nerves, Polycentrus is a moderately generalized percoid. Compared with Roccus, Archoplites, Kuhlia, and Perca, it is more specialized in its lateral line system: the second to fourth infraorbitals apparently are fused as are the fifth and sixth, and only one canal neuromast is in each compound bone; there are more cephalic pitlines, and these have more organs: the trunk lateral line is reduced to one tubed scale but there are three longitudinal rows of scales bearing free lateralis organs (pitorgans), one row each along the bases of the dorsal and anal fins and one row halfway between the dorsal fin and the horizontal septum. These are innervated by dorsal and ventral segmental branches from a trunk lateral line nerve pattern of the basic acanthop- terygian type. No communis fibers from the vagus nerve join the ramus lateralis accessorius (RLA) on top of the head; RLA is composed only of communis fibers from the facial nerve; the same observation holds for other percoids and other groups examined. Therefore, it may be necessary to use the name ramus recurrens facialis in its place. Comparisons with other groups, especially some percoids. beryciforms. atherinomorphs. and paracanthopterygians, brought out specializations in these groups which made more evident the generalized state of the nerves of Poly- centrus. Whereas Polycentrus is generalized in its innervation of the snout, the carangids, rachycentrids, cory- phaenids, and echeneids have a shared specialization in prenasal canals and canal bones; a shared specialization rare in teleosts, of an evident migration of an anteriormost frontal canal organ into the nasal canal occurs only in the gadoids, ophidioids, and Stephanoberyx; a shared specialization, apparently unique to the group, of an evident capture of a free lateralis organ by the nasal bone occurs in all berycoid families; atherinomorphs have a shared specialization of a large general cutaneous nerve to the upper jaw, but it is present also in holocentrids; a unique specialization of the nasal canal occurs also in Scomber and Rastrelliger; whereas the cheek-muscle innervation in Polycentrus is not distinctive, it is in atherinomorphs and in various other groups. The pattern of innervation within a muscle mass as well as the source of innervation to the muscle may be of systematic importance. Of the four functional nerve-component systems, Polycentrus is specialized mostly in the lateralis system; the communis (gustatory) system is present in one of the basic percoid patterns of the recurrent facial nerve; nothing distinctive was observed in the motor system (gill-arch-muscle innervation was not compared) nor in the general cutaneous system. Generalizations drawn from observations of 85 families for the innervation of the snout and upper jaw are that (1) pitorgans on the snout and neuromasts of prenasal canals are invariably innervated from the infraorbital, not from the supraorbital trunk, and (2) general cutaneous innervation of the upper jaw is only from the infraorbital trunk (except in atherinomorphs and the holocentrids), not from the supraorbital trunk as might be expected. Reasons for utilizing cranial nerves in higher category classification are given along with suggestions for simplifying cranial nerve studies. Introduction In the 1960's there was a notable renewal of interest in problems of the classification of bony fishes at higher taxonomic levels. Numerous or- ders were shifted into new systematic positions (Rosen 1964; Greenwood, Rosen, Weitzman, and Myers 1966; Rosen and Patterson 1969; Ro- sen 1973). An increase in the number of higher taxonomic categories was utilized to express new and more detailed views of relationships. Much of the new classification has been influ- enced by the methodology proposed by Hennig (1966) for phylogenetic systematics. The entire classification of fishes is due for reexamination under the impetus of new methods and renewed interest. The largest and a most formidable group, the order Perciformes, should receive major attention. One precept of an improved methodology of systematics should be that systematic informa- tion be drawn from several anatomical systems. Most past studies on higher category classifi- cation have utilized the skeletal system as the chief source of characters. Few have included the muscles and almost none the nerves (see Freihofer 1963). The muscles are now being used more extensively (Winterbottom 1974a and 1974b). The nerves, hopefully, will be also. A large obstacle to their use, the lack of a tech- nique for readily viewing the nerves, has been removed. Whereas the only way to study ac- curately the peripheral nerves has been by te- dious methods of serial sectioning and recon- struction, the nerves can now be seen in a whole specimen by means of the Sihler technique. The Sihler technique renders a whole or hemi- sectioned specimen virtually transparent except for the nerves, which are stained a dark purple. Descriptive nerve studies involving little more effort than for osteological studies are now prac- tical. The growth of a comparative literature on the nerves can begin. Of more immediate im- portance for getting at the taxonomic utility of the nerves than accumulating a nerve literature, which will take decades, is the formation of a reference collection of Sihler nerve prepara- tions. Such a collection can now be assembled relatively quickly, covering a sizeable taxonom- ic range. Assuming that properly preserved fish- es of numerous groups are available, an expe- rienced technician working one year can produce fine nerve preparations representing 50 to 100 or more families. Properly processed Sih- ler preparations (see under "Methods" section for use) may last 15 to 20 years and no doubt will last longer. The reference collection, once assembled and growing, can be used for con- ducting surveys of promising nerve complexes. Several nerve complexes were surveyed dur- ing the time this descriptive account of Polycen- trus was in progress. The results are in various stages of completion and are planned for later publication. The studies embrace comparisons ranging from Amia up to callionymids. Sihler nerve preparations representing up to 90 families were used. Two of the nerve complexes in- volved the innervation of lateral line canal bones; a third was a large general cutaneous nerve of the supraorbital trunk; a fourth in- volved patterns of innervation to the cheek mus- cle mass; a fifth concerned new patterns of a gustatory nerve, the recurrent facial; and the sixth was on trunk lateral line nerve patterns. Each of these studies revealed nerve charac- ters of promising systematic importance. A few are apparently convergent in some groups. Two attributes of nerves giving them systematic po- tential were observed in these studies. One is that nerves follow their end organs (taste buds, lateral line canal organs, and muscles). The oth- er is that, in general, each nerve innervating a lateral line canal neuromast has a certain mor- phological integrity connected with that bone and organ. No other nerve to a canal neuromast may enter through the substance of that bone and supply a canal organ there. This observation might be stated as a rule. As with all rules, they are always (it seems) occasionally broken, but there are always good reasons for their being broken; the exceptions to the rule, if the excep- tions are valid, should prove the rule. Important for the systematist using nerves is the fact that the exceptions result in new specializations being formed. These may become characters useful to the systematist. If nerves always fol- lowed the rules, there would be fewer important systematic characters. Some examples of what nerves do that are important to systematists come from study of the nerves and neuromasts of the canal bones. Not only may the total number of canal organs be significant for a main branch of the cephalic canal system, but the changes in the number of organs in each canal bone may be especially im- portant. These changes involve how canal or- gans in a bone may increase or decrease in num- OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 her. An increase in the number of organs may result from an original organ dividing into two organs which subsequently move away from each other; an organ may migrate out of its bone into another canal bone; a canal bone may, in effect, '"capture" an adjacent terminal free lat- eralis organ. Unless the innervation to the canal organs is studied, the systematic significance of the canal bones may largely or completely es- cape detection. Such facts as these plus the fact that the cra- nial nerves of more than 20,000 species of fishes remain to be explored should make the study of nerves of fishes a rather exciting prospect to some systematists. The order Perciformes, to which Polycentrus belongs, has been divided into as many as 20 suborders (Greenwood et al. 1966) and may con- tain up to 7,000 species. The present report is the only detailed description of the fifth, sev- enth, ninth, and tenth cranial nerves of a mem- ber of this order. Accounts are needed of the cranial nerves of representatives of the other suborders, though descriptions need not be as detailed as this one for Polycentrus \ Descriptive reference studies break the ground for ensuing comparative studies in which the mass of detail need not be reported, but only the significant differences between compared species. This re- port on Polycentrus will, hopefully, serve such a purpose for the suborder Percoidea. Methods The courses of the cranial nerves are de- scribed mainly from whole specimens cleared and stained selectively for the nerves by the Sih- ler technique. For use of the method see Wil- liams (1943), Freihofer (1966), Fraser and Frei- hofer (1971), and Freihofer et al. (1977). All myelinated nerves are stained down to very small branches. A much more accurate and complete picture of the distribution of the nerves is possible by this method than can be had from serial sections. The latter method should be used for study of the complexes of nerves and gan- glia, especially those inside the cranial cavity for which it is indispensable. It is best to use both methods. Much preliminary, exploratory work on the nerves can be done for systematic pur- poses, however, by use of the Sihler technique together with the study of the basic nerve ref- erences. The nerves are drawn in Figures 1 through 14 as white cords as accurately as possible on the background of the skeleton, the bones serving as reference points for the courses of the nerves. This seems the natural way to illustrate the nerves for use by systematists. The major nerve components are not drawn upon the nerves. Usually, so many components would have to be crowded into the space of each nerve and its branches that the distribution of the nerves could not be shown in the detail that they now are. The probable components for all the nerves and their branches are given in the text. One serious problem with the preservation of specimens for Sihler processing should be em- phasized. The problem is that manufacturers of formaldehyde now leave from 10 to 15% methyl alcohol in it for the purpose, they say, of "pres- ervation of the preservative," for retarding the breakdown of formaldehyde into paraformalde- hyde. Even reagent-grade formaldehyde has this amount of alcohol in it. The only grade of form- aldehyde that I have been able to obtain that can compare with the purity of the formaldehyde I used before 1969, which had 1% or less alcohol content, is the grade sold as "purified formal- dehyde." Thus far, I have succeeded in obtain- ing it only in 55-gallon drums. Specimens pre- served in the other grades of formaldehyde are ruined for use in the Sihler technique. It is pos- sible to make formaldehyde free of alcohol by heating paraformaldehyde crystals in water, us- ing as a catalyst a drop or two of ammonium hydroxide solution (28% NH3). Since the intracranial courses and ganglia of the nerves as well as the brain are destroyed while macerating Sihler specimens in 2 or 3% aqueous potassium hydroxide solution, a serial- section technique was used to study these parts in Polycentrus . The object at the time the re- search was planned was to use a technique that would help clarify difficult points on ganglia and nerve anastomoses and to rely on published ac- counts to help resolve questions of nerve-fiber tracts and connections. The method chosen was Curtis's modification of Van Gieson's triple stain (Leach 1946). It was easy to use and gave brillantly stained and well-differentiated tissues. It is not good for fiber-tract study. All descriptions based on Sihler preparations are from one specimen unless otherwise indi- cated. The nerves for the gill arches and asso- ciated muscles are from a second Sihler speci- men. FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII Dissections of fresh formalin specimens were used to check against the serial sections on such points as the intracranial courses and ganglia of the trigeminal, facial, and vagal nerves. Skeletal preparations cleared and stained by the alizarin method of Hollister ( 1934) were used for making the drawings of the cranial skeleton. All skeletal drawings were made from one spec- imen (CAS 12540) from Guyana. The muscle terminology follows that of Win- terbottom (1974a). The nerve terminology gen- erally follows that of Herrick ( 1899). In the pres- ent work, lateralis organs are referred to as canal neuromasts if located in canals and as free lat- eralis organs or pitorgans if located in skin out- side the canals. The term pitline is used to in- dicate a row of free lateralis organs, or even a single organ if that is all that is present in any area, whether or not these organs are in pits. The term nerve is loosely used to refer to an entire cranial nerve and its branches or to a bun- dle of nerve fibers of any size coursing inde- pendently outside of the brain or spinal cord. The root or radix of a cranial nerve is the prox- imal part or parts of the nerve inside the cranium and close to the brain. A nerve root is either sensory, and of a single functional component, or motor in function. Herrick, in his work on Menidia (1899), Gad- us (1900), and Ameiurus (1901), used a modifi- cation of the Weigert method for preparation of serial sections of nerves. The modification worked excellently for Herrick, but he found te- leost tissues to be very brittle for sectioning (see Herrick 1898, and Sheldon 1914). The fixatives required a hardening time of up to 6 months and the use of osmic acid (osmium tetroxide). Using fiber diameter as a means of identifying the four nerve components, Herrick was able to follow on his serial sections the fiber bundles of the different functional components of the nerve roots, from the brain through the ganglia and out to their undifferentiated endings or end organs. His Menidia paper (1899) is still the best single reference on the nerves of fishes. Literature on Nerves of Perciform Fishes Relative to the great size of the order Perci- formes, there are very few descriptive studies of the nerves of perciform fishes. Stannius (1849) and Baudelot (1883) gave observations on var- ious cranial nerves of some perciforms. Cuvier and Valenciennes (1828) described the cranial nerves of Percafluviatilis from dissections. Allis (1903) carefully described the nerves of the mackerel, Scomber scomber , but not completely nor in much detail. Maheshwari ( 1965) described the cranial nerves of the spiny eel, Mastacem- belus armatus, and Saxena (1969a) did likewise for the nandid, Nandus nandus, but both of these authors used only dissection methods and omitted details in their descriptions, diminishing the systematic usefulness of their work. The most useful references for this study were the papers by Herrick (1899, 1900, 1901), espe- cially his monograph (1899) on the cranial nerves of Menidia (family Atherinidae). His Menidia paper pioneered the analysis of nerves of fishes according to the major types of functional nerve fibers they carry. The nerve components, as Herrick called the functional types of nerve fi- bers (see section on nerve components below), are the best basis for analyzing, identifying, and understanding the nerves. Other papers found useful because they were so carefully and thor- oughly done were those by Allis (1897, 1903, 1910) on the bowfin, Ainia calva, the mackerel. Scomber scomber, and on Scorpaena: Norris (1925) on the genera Acipenser, Polyodon, Amia, and Lepisosteus: Norris and Hughes (1920) on the spiny dogfish, Squalus acanthias; Pancratz (1930) on the toadfish, Opsanus tau; Manigk ( 1934) on Phoxinus; and, lastly, the most recent study by Ray (1950) on Lampanyctus. Since 1960 the following authors published general descriptive accounts on some or all of the cranial nerves of fishes: Freihofer (1963, 1970, 1972); Gilmore (1972); Gupta (1972); Ma- heshwari (1965); Mithel (1964a, 1964b); Nara- wane (1965): Saxena (1966, 1967, 1969a, 1969b): Saxena and Rastogi (1968): Springer and Frei- hofer (1976); Vashisht and Uberoi (1965). In all these studies except my own, in which serial sections and/or Sihler whole-nerve preparations were used, dissection of preserved specimens was the only technique employed. Family Nandidae Polycentrus schomburgkii Miiller and Tros- chel, 1848, is a small spiny-rayed fish living in fresh water in northeastern South America and Trinidad. It belongs to the family Nandidae, which is one of about 70 families of the suborder Percoidea, probably the least specialized of the 20 recognized suborders of the order Perci- OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 formes (Greenwood et al. 1%6), with perhaps 7,000 species. Polycentrus is specialized for stalking its prey. Its barely perceptible swimming movements and coloration make it look rather like a dead, float- ing leaf when approaching its prey fish. After an investigative forward movement, instead of turning around and swimming away, Polycen- trus usually swims backwards and downwards, which it can do for some distance unobtrusively. The lateral line shows specialization seemingly for these ways of swimming. The large, protru- sible jaws are adapted for suddenly engulfing the prey. Liem ( 1970) has done a comparative func- tional anatomical study of the feeding mecha- nism of the Nandidae. In the rest of its mor- phology, except for the increase in number of dorsal and anal fin spines, Polycentrus appears to be a generalized percoid. The Nandidae are of special zoogeographical interest. There are two monotypic genera (Af- ronandus and Polycentropsis) in Africa, two monotypic genera {Polycentrus and Monocir- rhits) in South America, and one genus, the least specialized (Nandus), with 2 species in India and Southeast Asia. The ancestors of the African and South American genera were evidently liv- ing in the area of separation between Africa and South America when these continents drifted apart. Names of Cranial Nerves There are actually eleven pairs of cranial nerves in fishes, not ten. The nervus terminalis, which has the number zero, was not discovered (Pinkus 1894) until long after the other ten pairs had been numbered. The present terminology for the cranial nerves may not be the best that could be devised, but it is so well established in the literature of vertebrates that it can hardly be uprooted. Cranial Nerve Number Name 0 nervus terminalis 1 nervus olfactorius (olfactory) II nervus opticus (optic) III nervus oculomotorius (oculomotor) IV nervus trochlearis (trochlear) V nervus trigeminus (trigeminal) VI nervus abducens (abducent) VII nervus facialis (facial) Cranial Nerve Number Name VIII IX nervus acusticus (auditory. acoustical) nervus glossopharyngeus (glossopharyngeal) nervus vagus (vagal) Nerve Components Herrick (1897, 1899, 1903) used a simple func- tional analysis in describing the cranial nerves of Menidia. His system is followed here for the cranial nerves of Polycentrus. Each root of a nerve is considered to be com- posed of one functional component. Cranial nerves I (olfaction), II (vision). III (motor), IV (motor), VI (motor), and VIII (acousticolater- alis) are very simple in that each has character- istically only one main functional component which is either sensory or motor. The other cra- nial nerves are more complex, containing one or more sensory and one motor root. A sensory root is either lateralis (acousticolateralis), com- munis, or general cutaneous in its functional component. These components are defined be- low. Cranial nerve V (trigeminus) has two roots: one motor and one general cutaneous; nerve VII (facialis) has four roots: two are lateralis, one is communis, and one is motor: nerve IX (glos- sopharyngeus) has two roots in most fishes: one motor and one communis; nerve X (the vagus together with the lateral line nerve of the trunk) has four roots: one motor, one lateralis, one communis, and a small general cutaneous root. The cranial nerve roots are easy to follow in their courses from the brain out to the first cra- nial nerve ganglia, but at this point inside the cranium where most of the cranial ganglia are located, nerves V, VII, and X begin to form an- astomosing complexes, one of which is the tri- gemino-facialis complex. This complex forms intracranially near the closely spaced trigeminal and facial foramina of the prootic bone. Four sensory roots and their ganglia and two motor roots are more or less intimately compacted. All necessary fiber interchanges are made there. Three main nerve trunks arise from the trigem- ino-facialis complex: the truncus supraorbitalis, truncus infraorbitalis, and truncus hyomandib- ularis, as well as the palatine nerve. The cranial nerves of Polycentrus are ana- FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGK1I lyzed into functional components as far as pos- sible. In instances where the component could not be determined directly, its identification was made indirectly on the basis of Herrick's work on Menidia . Definitions of the five functional components found variously in cranial nerves V, VII, IX, and X are listed below. Each sensory compo- nent is referred to as a system of similar fibers. 1. General cutaneous system. General cuta- neous fibers innervate skin: in fishes they do not innervate specialized sense organs; they end only in free nerve terminations. The cell bodies are located in the Gasserian ganglion. Their fibers terminate in the cen- tral nervous system in the spinal V tract or the cells associated with it. General cuta- neous fibers are part of the somatic sensory system. 2. Communis system. Communis fibers inner- vate taste buds on the lips, in the buccal and pharyngeal cavities, and wherever taste buds occur on the external surface of the body (head, fins, and trunk). The cell bodies for communis fibers are located in the geniculate ganglion. For the vagus and glossopharyngeus nerves, a second kind of fiber is associated with the communis sys- tem. These are fibers that have free, un- differentiated endings in the mucous epi- thelium of the pharyngeal and buccal cavities. Communis fibers end in the brain at a single center, the lobus vagi of the medulla oblongata. Communis fibers may enter this center directly through the vagus roots or indirectly through the fasciculus communis tract from the roots of the 9th and 7th cranial nerves. Communis fibers belong to the special viscerosensory sys- tem. 3. Acousticolateralis system. Its fibers inner- vate the lateral line organs and the internal ear. They terminate in the tuberculum acusticum of the medulla oblongata. The fibers belong to the special somatosensory system. 4. Somatomotor system. On the head, fibers of the somatomotor system innervate the extrinsic eye muscles (the four rectus and two oblique muscles) and are carried in the 3rd, 4th, and 6th pairs of cranial nerves. 5. Visceromotor system. On the head, fibers of the visceromotor system innervate mus- cles of the jaws and gill arches and are car- ried in cranial nerves V, VII, IX, and X. This component in the present paper is usually simply referred to as motor, since only the jaw and gill-arch muscles are dis- cussed. Descriptions of Nerves Radix Profundus Closely associated at the brain with the root of the fifth, or trigeminal, nerve, but separate from it, is the radix profundus (Figs. 14 and 31). The radix profundus supplies visceral sensory innervation to muscles which move the lens and change the diameter of the iris. This nerve di- vides into two diverging rami, the ramus ciliaris longus and the ramus ciliaris brevis (called the radix longus up to the point of its contact with the ciliary ganglion). Both rami receive major fibers from the fifth, or trigeminal, sympathetic ganglion and separately enter the rear of the eye- ball. In one specimen of Polycentrus , the radix pro- fundus has its root origin in the medulla at the dorsal surface of the base of the trigeminal root. Both the profundus and the trigeminal roots emerge from the midlateral wall of the anterior end of the medulla, ventral to the posterior ends of the optic lobes and a little posterior to the root of the nervus trochlearis. The radix profun- dus remains separate from the trigeminal root for the rest of its intracranial course. In another specimen the radix profundus was applied closely to the trigeminal root for some distance from the brain, after which the two roots sepa- rated. En route to its cranial exit, the radix profun- dus lies fairly close to the nervus trochlearis, both nerves usually being on the dorsal surface of a large blood vessel, with the profundus me- dial and a little ventral to the trochlearis, and both roots being medial to the roots and ganglia of the trigeminal and facial nerves. Not far from its cranial exit, the radix profundus bears on its dorsal surface a ganglion of about two dozen cell bodies (Fig. 14). Shortly beyond its ganglion, the profundus, now called the truncus ciliaris pro- fundus, is crossed dorsally by the intracranial parietodorsal branch (RLA-PD) of the ramus lat- eralis accessorius (RLA). Shortly beyond this point, the truncus ciliaris profundus enters the trigeminal foramen, passing through it at the dor- solateral corner of the foramen. The truncus is OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 pressed up against the wall of the foramen by the large dorsal fiber mass of the truncus su- praorbitalis. The truncus ciliaris profundus moves down to lie ventral to the large horizon- tally elliptical fiber mass of the fifth-seventh complex that is pressed up against the prootic roof of the depression (the trigeminofacialis fos- sa of Allis) in which the external part of the fifth- seventh complex lies. The truncus ciliaris pro- fundus divides into two parts. The lateral divi- sion is the ramus ciliaris longus, and the medial division is the ramus ciliaris brevis. The ciliaris longus receives a sizeable bundle of fibers from the trigeminal sympathetic ganglion lying below it. The ciliaris brevis passes ventrally and then medially through or past the trigeminal sympa- thetic ganglion, apparently receiving sympathet- ic fibers from it. On the left side of the specimen, trigeminal sympathetic nerve fibers clearly could be seen entering the ciliaris brevis, but not on the right side (Fig. 14). Leaving the trigeminal sympathetic ganglion, the ciliaris brevis, which at this point can be termed the radix longa ad ganglion ciliare or radix longa, passes medially over to the ventrolateral surface of the oculo- motor nerve, which lies on top of a large blood vessel or sinus close to the prootic wall of the cranium. Some ganglion cells form at the point of contact between the oculomotor and the radix longa (Fig. 14). The radix longa courses for a short distance with the oculomotor nerve, and the two separate and each passes ventrally down opposite sides of a large blood vessel, the radix longa passing down the lateral side and the oc- ulomotor down the medial side. About two- thirds of the way down the lateral side and after the formation of a few more ganglion cells in it, the radix longa passes medially around the large blood vessel and joins the ciliary ganglion lo- cated on the oculomotor nerve. The ramus cil- iaris brevis directly departs from the ciliary gan- glion and passes anterodorsally and laterally over to the rear of the eyeball in company with an ophthalmic blood vessel and penetrates the sclera close to the optic nerve and vein. Inside the sclera the ciliaris brevis passes ventrally on the side of a large vein or sinus reaching the lateroventral edge of the retina where the re- tractor lentis muscle attaches to the base of the iris (Fig. 15). The ciliaris brevis sends a branch anteriorly and another posteriorly along the pe- riphery of the iris, each branch ramifying over the ventral surface of the iris. The remainder of the ciliaris longus is de- scribed next. At the point where it has received fibers from the trigeminal sympathetic ganglion, the ciliaris longus shortly leaves the proximity of the fifth-seventh complex and passes anter- oventrally through the fibrous coating separating the prootic foraminal area from the orbital cav- ity, enters the orbital cavity in company with an ophthalmic artery, passes laterally over to the dorsal rear of the eyeball, and enters the eyeball about two-thirds of the way middorsally above the entrance of the optic nerve (Figs. 14 and 15). The course and relationships of the radix pro- fundus are essentially the same on both sides of the sectioned specimen. Fifth and Seventh Cranial Nerve Roots, Trunks, and Rami The trigemino-faeialis complex is the result of six roots of the fifth and seventh cranial nerves (each nerve root carrying fibers of one functional component) coming together, forming ganglia if they are sensory roots, exchanging fibers, and then leaving again with nerve components re- combined into the three main nerve trunks which innervate the anterior half of the head. These three nerve trunks are the truncus su- praorbitalis, truncus infraorbitalis, and truncus hyomandibularis. The truncus supraorbital courses anteriorly from the rear of the orbital cavity dorsal to the eye and innervates the top of the head and the snout (Fig. 3) but not, except rarely, the upper jaw. The infraorbital trunk passes anteriorly from the rear of the orbital cavity along the ventral edge of the orbit and branches into three main rami: 1) the ramus maxillaris trigeminus to the upper jaw; 2) the ramus buccalis facialis to the lateral line organs associated with the infraorbital canal and to the adjacent skin; and 3) the ramus mandibularis trigeminus to the muscles and skin of the cheek and lower jaw (Figs. 1, 6-10). The truncus hyo- mandibularis facialis leaves the cranium a little further posteriorly than do the first two trunks and passes ventrally along or through the hyo- mandibular and preopercular bones and divides into two main rami, the ramus mandibularis fa- cialis and the ramus hyoideus (Figs. 2 and 13). The ramus mandibularis innervates the preoper- cular area, the anterior part of the opercular area, and the lower jaw. The ramus hyoideus passes down the hyoid arch innervating the skin and muscles of the gill membrane and branchio- FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBVRGKII stegal rays, and the posterior part of the pro- tractor hyoidei muscle connecting the hyoid arch to the lower jaw. The six roots of the 5th— 7th complex of fishes may be examined more closely. The 5th or tri- geminal nerve consists of two nerve roots, a so- matic sensory root carrying nerve fibers belong- ing to the general cutaneous system and a visceral motor root carrying motor fibers to jaw muscles associated originally with an anterior gill slit lost in the evolution of the jaws. The 7th or facial nerve has four nerve roots, three of which are sensory and one motor. The motor root supplies visceral motor fibers to the mus- cles of the palate, opercle, and hyoid arch — muscles associated originally with the hyoid gill arch which are innervated by the 7th cranial nerve. The three sensory roots of the facial nerve consist of two lateralis roots, referred to as the dorsal and the ventral lateralis roots; the third is a visceral sensory root carrying fibers that innervate the taste buds and the mucosa of the mouth. Each of the sensory roots of the 5th and 7th nerves bears a large ganglion. After leaving the posterior part (medulla ob- longata) of the brainstem, the six roots of the 5th and 7th nerves converge anteriorly towards their foramina in the prootic bone, but shortly before passing through the prootic, a ganglion forms on three of the sensory roots of the facial nerve. In Polycentrus the Gasserian ganglion of the sensory root of the trigeminal nerve forms directly outside of the trigeminal foramen in the prootic bone. In some other fishes it forms inside the cranium. Just beyond the ganglia but still inside the cranium, the fiber bundles in all fishes begin to detach from the roots, the various fiber bundles coming together forming the three nerve trunks described above. In Polycentrus the dorsal lateralis root of the 7th cranial nerve sends a large bundle of fibers into the supraorbital trunk, and the remainder of the root enters into the formation of the in- fraorbital trunk. The rest of the supraorbital trunk is formed by a bundle of general cutaneous fibers from the Gasserian ganglion of the 5th cra- nial nerve and a small bundle of communis (taste fibers) from the geniculate ganglion of the gus- tatory root of the 7th cranial nerve. This com- munis bundle then leaves the supraorbital trunk as the orbito-pectoral branch of the recurrent facial nerve. In addition to the large bundle of lateralis fi- bers from the dorsal root of the 7th cranial nerve, the infraorbital trunk receives a large bundle of general cutaneous fibers from the Gas- serian ganglion for the skin. It also receives the whole of the motor root of the 5th cranial nerve. Both of these trunks, the truncus supraorbitalis and truncus infraorbitalis, leave the cranium through the trigeminal foramen on the outer face of the prootic bone and then diverge on the rear wall of the orbital cavity, one trunk passing dor- soanteriorly above, the other ventroanteriorly below, the orbit. The truncus hyomandibularis in Polycentrus is formed by the whole of the motor root of the 7th cranial nerve, plus a large bundle of com- munis fibers from the geniculate ganglion of the 7th cranial nerve, and by the whole of the ven- tral lateralis root of the 7th nerve. The truncus hyomandibularis usually contains a sizeable bundle of general cutaneous fibers from the Gas- serian ganglion. These fibers reach the truncus hyomandibularis as the ramus communicans n. trigemini ad n. facialem. This ramus passes pos- teriorly in a chamber or lateral passageway that lies in the wall of the prootic between the tri- geminal and facial foramina. The ramus com- municans turns laterally beyond the prootic chamber and joins the truncus hyomandibularis as this trunk enters its passageway in the hyo- mandibular bone. Not all of the communis fibers of the genicu- late ganglion of the 7th cranial nerve go into the three trunks of the 5th and 7th cranial nerves. Some geniculate fibers form the ramus palatinus, which passes out of the cranium into the myo- dome and then along the medial edge of the pal- ate next to the parasphenoid bone, innervating taste buds and the mucosa of the palate and up- per jaw. In many fishes there are still other gus- tatory branches arising from the geniculate gan- glion. These are considered together under the terms ramus lateralis accessorius (ramus recur- rens facialis). The branches of this ramus course back from the head onto the trunk. As will be seen in the detailed descriptions for Polycentrus , both the ramus mandibularis trige- minus of the truncus infraorbitalis and the ramus mandibularis facialis of the truncus hyomandi- bularis course onto the lower jaw and out to its tip. Although the trigeminal (fifth) and facial (seventh) nerves parallel each other in their courses on the lower jaw, each nerve serves a different function there. Where these rami reach OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 the lower jaw in Polycentrus and in teleosts in general, the ramus mandihularis trigeminus car- ries only motor fibers for muscles and general cutaneous fibers for the skin of the lower jaw, while the ramus mandibularis facialis carries on- ly lateralis fibers for free lateralis organs and canal neuromasts, and communis fibers for the taste buds and mucosa of the lower jaw. Roots and ganglia of nervus trigeminus The single sensory root and single motor root of the nervus trigeminus (V) are indistinguish- ably bound together as they arise from the mid- lateral wall of the medulla oblongata directly posterior to the root of the oculomotor nerve, anterior and ventral to the facial roots, and pos- terior to the lateral emergence of the nervus trochlearis (Fig. 29). The radix profundus lies on the dorsal surface of the trigeminal root as these two roots leave the brain. They soon separate but remain rather close for most of their intra- cranial courses. The trigeminal root remains un- connected to the roots and ganglia of the facialis. When close to its foramen, the compound motor and sensory trigeminal root lies dorsal to the geniculate ganglion of the facial nerve and me- dioventral to the dorsal lateralis ganglion of the facial nerve. The Gasserian ganglion of the tri- geminal nerve forms outside the trigeminal fo- ramen where the final interchanges between the trigeminal and facial nerves occur to form the truncus supraorbitalis and truncus infraorbitalis. The communis root and geniculate ganglion The communis root of the facial nerve carries gustatory fibers to taste buds in the mouth and to terminal buds on the body, and communis fibers to the mucosa of the buccal cavity. Dorsal to the facial foramen, the communis root en- larges into a round, dense mass of large and small ganglionic cells, the geniculate ganglion (Fig. 31). From the geniculate ganglion arise two ventrally directed, large fiber bundles; one is the anterior ramus palatinus which innervates taste buds on the palate and upper jaw, and the other is the communis bundle which joins the truncus hyomandibularis as this nerve passes through the facial foramen. Several fiber bundles leave a dorsoanterior extension of the geniculate ganglion. One of these is a small bundle, the parieto-dorsal branch of the ramus lateralis accessorius (Fig. 31), which passes laterally around the ventral surface of the trigeminal root and then dorsally up the side of a blood vessel where it is joined by a similar bundle from the medial side of the geniculate ganglion. The enlarged nerve thus formed shortly comes into contact with the in- tracranial ganglion of the radix profundus and then passes dorsally up to the parietal bone, through which it passes. The further course of the parieto-dorsal branch of the ramus lateralis accessorius (RLA), is described in another sec- tion. There is no fiber exchange between the parieto-dorsal branch of the RLA and the radix profundus. The remainder of the dorsoanterior part of the geniculate ganglion gives rise to a fiber mass which passes through the trigeminal foramen, lying, as it does so, on the lateral sur- face of a mass of trigeminal fibers. As this com- munis bundle goes out the trigeminal foramen. it detaches fibers that course with the ramus oticus. These fibers of the geniculate ganglion constitute the orbito-pectoral branch (Fig. 31, RLA-OP) of the RLA. General cutaneous fibers leave the Gasserian ganglion outside the trigem- inal foramen and also join the ramus oticus. On serial sections no fiber bundle from the genicu- late ganglion was observed to pass into the in- fraorbital trunk, but on a dissection a fiber bun- dle from the geniculate ganglion appears to enter the infraorbital trunk, and another apparently enters the supraorbital trunk, but it could not be definitely determined that they do. In summary, the fiber bundles leaving the ge- niculate ganglion and joining various parts of the trigemino-facialis complex are as follows: (Da large bundle of fibers that forms the ramus pal- atinus; (2) a large bundle to the truncus hy- omandibularis; (3) a dorsally directed intracra- nial branch (the parieto-dorsal branch of the RLA) to the dorsal fin; (4) a sizeable bundle that forms the orbito-pectoral branch of the RLA to the pectoral, pelvic, and anal fins; (5) a sizeable bundle, probably to the infraorbital trunk, and a small bundle, probably to the supraorbital trunk. Herrick ( 1899: 351) states that in Menidia such fibers in small numbers enter the supraor- bital trunk. Dorsal lateralis root of the facial nerve The dorsal lateralis root forms a rather large ganglion of from small- to large-sized, compactly grouped cell bodies. On its course to its ganglion (Fig. 31), the dorsal lateralis root lies on the medial side of the internal ear and is lateral and FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKI1 dorsal to the trigeminal root. The ganglion is directly posterior to the intracranial profundus ganglion and medial to the geniculate ganglion. The dorsal lateralis root leaves the cranium at the dorsal corner of the trigeminal foramen. Out- side the cranium, part of the root turns antero- dorsally and continues against the side of the cranium as a part of the truncus supraorbitalis. Some fibers of the dorsal lateralis root leave it and pass dorsally as part of the ramus oticus. A sizeable portion, probably half of the dorsal lat- eralis root, leaves the root as it passes out the trigeminal foramen and crosses to the lateral side of the trigemino-facialis complex (Fig. 31); this portion then passes ventrally to become the ramus buccalis facialis of the infraorbital trunk. Gasserian ganglion of the nervus trigeminus The Gasserian ganglion lies entirely outside the cranial cavity in Polycentrus and is separate from other ganglia near it except the trigeminal sympathetic ganglion, with which it has a fiber connection (Fig. 31). The radix profundus (called the truncus ciliaris profundus after for- mation of its ganglion) passes into the dorsolat- eral part of the Gasserian ganglion and divides into the ciliaris longus and ciliaris brevis while inside the Gasserian ganglion. Gasserian cells fill spaces between fiber bundles of the trigeminal and facial roots which are effecting fiber bundle exchanges and which form the truncus supraor- bitalis and truncus infraorbitalis. One arm of Gasserian cells extends dorsoanteriorly over the anterior surface of the dorsoanteriorly ascending truncus supraorbitalis, reaching almost as far as the first lateralis branch of the supraorbital trunk. A shorter, thicker arm of cells extends along the anterior surface of the truncus infraor- bitalis. The lateralis fibers from the intracranial dorsal lateralis ganglion and the communis fi- bers from the geniculate ganglion of the facialis nerve pass anteriorly behind the Gasserian gan- glion cells and form part of the supraorbital trunk. The rest of this trunk is formed by fiber bundles from the Gasserian ganglion constitut- ing the general cutaneous component. Lateralis and communis fiber bundles from the facial roots, plus all the trigeminal motor fibers, and a large number of cutaneous fibers from the Gas- serian ganglion all join and pass ventrally behind the Gasserian ganglion to form the infraorbital trunk. Roots and ganglia of the nervus facialis The nervus facialis arises by four roots which are fused basally giving the appearance of one root (Fig. 29). A short distance from the medul- la, the basal root separates into three parts which, however, represent four facial roots, the motor facial and the ventral lateralis facial roots being so close together as to appear as one root (Fig. 31). The facial roots emerge from the me- dulla directly dorsal and a little anterior to the anteriormost auditory root. The facial roots are as follows, starting dorsally: the dorsal lateralis root; the communis root, which enlarges ante- riorly into its geniculate ganglion; the motor root: and, most ventral, the ventral lateralis root, which arises directly ventral or medial to the anteriormost auditory root. A short distance from the brain, this ventral lateralis root comes to lie on the ventral surface of the motor root. These two roots become indistinguishably bound together. More anteriorly they leave the cranium as the truncus hyomandibularis through the facial foramen in the prootic bone. Before joining the motor root, the ventral lateralis root receives a ramus which is connected to the last two auditory roots. An intracranial connection between the auditory and facial nerves is appar- ently common in fishes, being found in Menidia (Herrick 1899), Lampanyctus (Ray 1950), and Scomber (Allis 1903). All these facialis roots near their points of origin lie over the posterior end of the lobus inferioris of their side. All the roots run anteroventrally to the trigemino-faci- alis foramina, where their relationships become complex in the formation of the supraorbital, in- fraorbital, and hyomandibular trunks. A few ganglion cells appear on the medial side of the ventral lateralis root a short distance after the ramus from the auditory roots joins its lateral surface (Fig. 31). A little further distally the ven- tral lateralis and motor roots join and many gan- glionic cell bodies appear on the lateral surface of the compound root, but they do not form as dense and compact a mass as occurs in the ge- niculate or Gasserian ganglia. The ganglionic cell bodies which are most abundant on the ven- tral half of the joined motor and lateralis roots (Fig. 31) are part of the ventral lateralis root. Beyond the ganglion the compound trunk of motor facialis and ventral lateralis roots passes medial to the intracranial flange of the prootic, which separates the facial and trigeminal fora- OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 mina, receives communis fibers from the genic- ulate ganglion, and, as the truncus hyomandi- bularis, passes out the facial foramen. Ramus communicans of the nervus trigeminus The ramus communicans of the nervus trigemi- nus is large in Polycentrus and forms from the posterior end of the part of the Gasserian gan- glion that extends into the prootic chamber (Fig. 31). The ramus communicans runs posteriorly in this chamber, emerges close to the facial fo- ramen, but remains separated by large blood vessels from the truncus hyomandibularis as the latter truncus leaves the facial foramen. The truncus hyomandibularis and its ramus com- municans from the trigeminal nerve pursue sep- arate courses which converge laterally and ven- trally at the medial side of the hyomandibular bone, which they enter together and course in a passageway in this bone, the ramus commun- icans lying on the dorsal surface of the truncus as the two go into the hyomandibular. The fibers of the ramus communicans shortly become a part of the truncus and cannot further be fol- lowed separately on the serial sections. All of the ramus communicans was observed on a Sih- ler preparation of Liparis pulchellus (Liparidae) to leave the proximity of the truncus hyoman- dibularis, not having become attached to that truncus, and to constitute almost the entire ra- mus hyoideus. In Menidia (Herrick 1899; fig. 3) all of the ramus communicans enters the ramus hyoideus, none apparently entering the other main division of the truncus hyomandibularis, that is, the ramus mandibularis facialis. In Poly- centrus some general cutaneous fibers continue in the latter nerve also. Truncus Supraorbitalis The dorsal lateralis and communis roots of the facial nerve together with the general cutaneous root of the trigeminal nerve contribute to the formation at the trigeminal foramen of the fol- lowing nerves that constitute, or are associated with, the truncus supraorbitalis: (1) the ramus oticus (general cutaneous and dorsal lateralis components); (2) the orbito-pectoral branch of the ramus lateralis accessorius (communis fibers from geniculate ganglion); and (3) the truncus supraorbitalis (dorsal lateralis and general cu- taneous fibers and possibly some communis fi- bers). The supraorbital trunk separates into its two main rami, the ramus ophthalmicus super- ficialis trigeminus (general cutaneous fibers) and the ramus ophthalmicus superficialis facialis (lateralis fibers), shortly beyond the frontal com- missure of the supraorbital lateralis canal. Ramus ophthalmicus superficialis trigeminus and ramus ophthalmicus superficialis facialis The first branch of the truncus supraorbitalis is the ramus oticus (Fig. 3, ROT). It is consid- ered separately in the next section. The second branch of the truncus, SORB 2, supplies skin and certain scale pockets bearing free lateralis organs on the head dorsal to the orbital rim (Figs. 1, 3, and 5) and is assigned, therefore, to the ramus ophthalmicus superficialis facialis, al- though it carries some general cutaneous fibers. It detaches from the truncus a short distance after the orbito-pectoral branch of the ramus lat- eralis accessorius (RLA-OP) leaves from along- side the truncus. Branch SORB 2 runs dorsally a short way and penetrates the alisphenoid through a relatively large foramen. On other specimens the foramen for SORB 2 was occa- sionally in the sphenotic bone. Entering the cra- nial cavity, SORB 2 rises dorsally along the in- ner surface of the frontal bone. En route it is crossed by SORB 3 (Fig. 5) from the truncus supraorbitalis. SORB 3 passes through the fron- tal bone, and after crossing SORB 2, it joins with the parieto-dorsal branch of the ramus lateralis accessorius (RLA-PD). SORB 3 was absent on the other side of the specimen. Near the cranial roof, SORB 2 detaches several minute nerves which appear to innervate, in part, the meninges of the brain in the region dorsal and anterior to the anterior semicircular canal. Medial to the supraorbital canal, but at about its dorsalmost level, SORB 2 divides into SORB 2a and SORB 2b (Fig. 1). The smaller. SORB 2a. passes through the midmedial roof of the cranium, turns anteriorly, runs over the surface of the horizon- tal myoseptum between the dorsal and ventral cranial roof musculature, curves laterally over to the skin, turns posteriorly underneath it, and innervates free lateralis organs on one of the scale pockets. Intracranially SORB 2a gives off a tiny twig which appears to supply the men- inges. At the point of origin of SORB 2a, a larger branch, SORB 2b, runs intracranially dorsoan- teriorly and soon penetrates the frontal bone medial to the frontal sensory canal. It curves over the external surface of the canal and passes FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBVRGK11 laterally to skin over the posterior corner of the eye. Upon reaching the skin it divides into sev- eral branches. One branch passes onto the skin connecting the eye to the orbital rim and onto the cornea over the dorsoposterior quadrant of the eye (Fig. 16, COR 1). A smaller branch passes posteriorly and innervates a row of free lateralis organs on a scale (Figs. 5 and 17). A larger branch of SORB 2b passes anteriorly giv- ing off about five successive short twigs each of which innervates a row of free lateralis organs on the skin of one of the scales that lies above the orbital rim, the lateralis-bearing scales form- ing a row which extends anteriorly from near the dorsoposterior quarter of the eye up to the frontal canal pore located in the anterior half of the orbital rim. The twig to the pore of the fron- tal canal near the middle of the orbital rim in- nervates a cluster of free lateralis organs on the membrane covering most of the canal opening. The main body of SORB 2, at the point where it detaches SORB 2a and SORB 2b, continues intracranially in a posterior and slightly dorsal direction a little above the anterior semicircular canal and comes in contact with the ramus lat- eralis accessorius (RLA-PD) but is separable from it. SORB 2 passes through the parietal bone and through the thin flange of bone (Fig. 1) constituting the parietal ridge, breaking up in- to four branches in the ridge. These branches send twigs to various scale pockets, each scale pocket bearing a line of free lateralis organs (Fig. 17), the lateralis organ-bearing scale pockets to- gether forming a line of free lateralis organs leading posterodorsally towards the middorsal line and ending above the rear of the supraoc- cipital area. It could be seen on the Sihler prep- arations that the sprays which these twigs form on the scale pockets are supplying specialized sense organs rather than merely being free sen- sory nerve endings of general cutaneous fibers in the skin. One of the four branches sends a twig dorsally and posteriorly, a few of its fibers going to the two dorsal scale pockets of the ver- tical row supplied by the ramus supratemporalis vagi. The remaining fibers of this branch sepa- rate into numerous small fiber groups which cross or run for a short distance with the ramus lateralis accessorius (RLA-PD), located beneath skin on top of the head, but then leave this ra- mus and innervate a few scales, each posterior to the vertical row supplied by the ramus supra- temporalis vagi. These few scale pockets are much less strongly innervated than are those of the supratemporalis row. It is doubtful that they also bear free lateralis organs, but they could. The remaining branches of the truncus su- praorbitalis serve mainly the lateral line organs of the frontal and nasal canals (from the ramus ophthalmicus superficialis facialis) and the skin (from SORB 5 and SORB 6 of the r. oph. sup. trigeminus) near the canals. Especially interest- ing are the apparently lateralis branches, one from each of three of the four branches to the lateral line organs. There are patches of free lat- eralis organs where these branches (SORB 4, SORB 8, and SORB 11a, see Figs. 3 and 17) terminate in the skin. Each of these probable lateralis rami detaches from one of the branches that innervates a canal neuromast of the frontal or nasal bone and continues, usually rather far anteriorly, apparently to innervate free lateralis organs mainly over the anterior end of the or- bital roof. One of these branches, SORB 1 la (Fig. 3), detaches from the nerve (SORB 1 1) to the lateral line organ in the nasal bone and runs anteriorly in the canal some distance before it passes through the lateral wall of the canal and innervates the overlying skin. Its terminal branchings lie directly opposite those of a branch of SORB 6, which is apparently a com- pletely general cutaneous nerve. Since there is a patch of free lateralis organs in this area and since SORB 6 is apparently a general cutaneous branch, it seems likely that SORB 11a is a lat- eralis branch supplying these free lateralis or- gans. It is probably the usual relationship that the same lateralis branch that supplies a canal neuromast also supplies the free lateralis organs in the skin around the adjacent canal pore. After giving off SORB 2, the truncus is a broad, flat band of nerve fibers with no distinct bundles and is pressed close against the frontal bone in the orbital cavity. Shortly, it divides into two groups of fibers, a medial, slightly smaller one with many black nuclei, and a lateral, larger one with much lighter-stained fibers. These two divisions are the rami ophthalmicus superficialis trigeminus and facialis, respectively. The trunk at this point has come to lie near the medial side of the frontal canal, as this structure lies near the orbital rim. A lateralis branch, SORB 4 (Fig. 3), detaches from the facial part of the main truncus, enters the bone of the frontal canal, and bifurcates, one fork at a time entering the canal and innervating sensory canal organs 4 and 5 of OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 the supraorbital canal. The two organs lie close together posterior to the frontal commissure of the supraorbital canal. The branch to each canal organ detaches a slender ramus, which is prob- ably lateralis or perhaps both lateralis and gen- eral cutaneous in function. Each penetrates the frontal bone and innervates tissue near the or- bital rim. The truncus supraorbitalis continues anterior- ly and a little laterally, lying up against the roof of the orbital cavity underneath the frontal ca- nal, and gives off two branches (Fig. 3) of un- even size, SORB 5 and SORB 6, which together constitute most of the ramus ophthalmicus tri- geminus and are general cutaneous in function. The much smaller branch, SORB 5, curves lat- eroanteriorly close to the edge of the orbital rim where two small twigs detach, one of which was lost in the skin connecting the orbital rim to the eyeball; the other is distributed to the orbital surface bordering the rim. The rest of SORB 5 (Fig. 16), now labeled COR 2, continues in skin directly lateral to the orbital rim, until in the anterodorsal quadrant of the orbit it turns to- wards the center of the eye, giving branches to skin connecting the eye and orbital rim; the rest of COR 2, which is the larger part, goes to the conjunctiva and cornea. SORB 6, which is the major portion of the ramus ophthalmicus super- ficialis trigeminus (r. oph. sup. tri.), and the re- mainder of the truncus, which is equivalent to the ramus ophthalmicus superficialis facialis (r. oph. sup. fac; see Fig. 3), diverge rather sharply from each other, then, after some distance, ap- proach each other and continue to the anterior end of the orbital roof where they leave together and pass out onto the snout beneath the nasal bone. The r. oph. sup. tri. courses across the ventral surface of the frontal bone in the orbital cavity and the r. oph. sup. fac. courses in a bony canal beneath or to the side of the frontal canal. Shortly before leaving the orbital rim. SORB 6 detaches SORB 6a, which passes dorsoante- riorly up the medial side of the nasal canal and innervates skin overlying the junctions of the anterior end of the frontal canal and the poste- rior end of the nasal canal. The rest of SORB 6 continues anteriorly a little below the ventral side of the nasal canal. Two-thirds of the way along the nasal canal and at the ventrolateral side of it, SORB 6 gives off several branches. The first of these is a small branch, SORB 6b, which passes dorsally and innervates skin on the medial side of the nasal canal. It lies directly in front of the terminal branching of the lateralis branch SORB 11a from the main truncus su- praorbitalis. The next branch, SORB 6c, larger than the SORB 6b, passes around the medial side of the nasal bone, rises to the dorsal level of this bone, and innervates skin medial to and a little behind the anterior end of the nasal bone. The remainder (SORB 6d) of SORB 6 passes to skin in front of, and lateral to, the anterior narial opening. Here it bifurcates, the dorsal fork pass- ing medially around the front end of the nasal bone to innervate skin behind the head of the maxilla, the other fork passing anteroventrally towards the dorsal half of the shaft of the max- illa, where it innervates skin in front of the an- terior narial opening and below the nasal bone. Branches SORB 6b, 6c, and 6d are essentially the same on both sides of the specimen. There is no indication that these branches innervate free lateralis organs in their vicinity. The nu- merous free lateralis organs located near the na- rial and nasal canal openings (Fig. 19) are most- ly, if not completely, innervated by facialis fibers of the infraorbital trunk (Fig. 1). Further study is needed of the areas of the front end of the snout and nasal and narial openings where the truncus supraorbitalis and truncus infraor- bitalis meet. The rest of the truncus supraorbitalis. after detaching SORB 6, is the ramus ophthalmicus superficialis facialis, which carries mostly lat- eralis fibers but apparently also some general cutaneous fibers. The ramus, coursing in a bony passageway in the frontal bone, curves to lie medial to the frontal canal and gives off branch SORB 7 that courses along the orbital roof. SORB 7 shortly detaches branch SORB 7a that enters the frontal bone, curves medially and dor- sally around the frontal canal, continues cours- ing anteriorly along the medial side of the canal until, a short distance behind the posterior end of the nasal bone, it rises to the skin over the frontal canal and innervates it. It could not be determined if this branch is general cutaneous or lateralis or both. The rest of SORB 7 courses anteriorly along the lateral side of the frontal canal and divides into four diverging, anteriorly directed branches; two of these emerge on the dorsal surface of the head, supplying skin in front of the anterior pore of the frontal canal, one branch passing anteriorly across the floor of the pore. Another of the branches continues FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII 13 along the lateral side of the frontal canal and innervates skin at the ventroanterior corner of the anterior pore of the frontal canal. The two other branches pass anteriorly almost up to the end of the orbital cavity, where they penetrate the frontal bone and pass to the skin anterior to the frontal pore. These branches of SORB 7 all innervate skin, none apparently innervate free lateralis organs, as far as could be determined, and are classed as general cutaneous branches. Only a few scattered free lateralis organs are found in the anterior third of the supraorbital rim area. The ramus ophthalmicus superficialis facialis continues anteriorly in bone at the medioventral side of the frontal canal. Halfway along its or- bital course, it detaches branch SORB 8, which innervates the third supraorbital canal organ. Some distance further SORB 9, innervating the second supraorbital canal organ, is detached. At the point where SORB 6 touches it, the ramus ophthalmicus superficialis facialis gives off SORB 10, which rises dorsoanteriorly along the medial wall of the frontal canal. From SORB 10 a twig is sent to skin outside the frontal canal, the rest going dorsally to innervate skin dorsal to the posterior end of the nasal bone. Directly beyond this branch, a smaller branch (not illus- trated) is sent to skin a little anterior to the pre- ceding branch. Branch SORB 10 apparently car- ries cutaneous fibers of the trigeminal ramus rather than lateralis fibers of the facial nerve. The ramus ophthalmicus superficialis facialis next passes through the frontal bone and contin- ues medial to the nasal canal which it penetrates and detaches SORB 11 which innervates SO 1, the first canal neuromast of the supraorbital ca- nal and the only lateral line organ in the nasal canal. Extending beyond SORB 1 1 is a thick, straight branch, SORB 11 A, which runs antero- laterally, penetrates the lateral wall of the nasal canal two-thirds along its length, and ends in a darkly stained spray of terminal fibers on the surface of the skin on the side of the canal. Free lateralis organs are located in this area, which SORB 1 1 A apparently innervates. Truncus Infraorbitalis The truncus infraorbitalis has three main di- visions: division IOl, the ramus buccalis faci- alis; division 102, the ramus mandibularis tri- geminus; and division 103 the ramus maxillaris trigeminus. Divisions 102 and 103 are closely bound together for some distance after leaving the area of the trigeminal foramen. Ramus buccalis facialis Division IOl, the ramus buccalis facialis, car- ries mainly lateralis fibers innervating the canal organs of the infraorbital series of bones, these lateralis fibers having come from the dorsal lat- eralis root of the facial nerve. InPolycentrus the ramus buccalis also carries a general cutaneous component, the fibers of which come from the Gasserian ganglion of the trigeminal nerve. They supply the skin of the cheek area and preoper- cular regions as well as skin on or near the in- fraorbital bones. The lateralis fibers of the ramus buccalis supply four canal neuromasts enclosed within the lachrymal canal as well as a neuro- mast enclosed in the canal of each of the second and third bones of the infraorbital series (Figs. 1 and 3). The fourth infraorbital, that on the sphenotic bone, has its neuromast innervated by a branch of the ramus oticus, a nerve which is not considered by Herrick (1899) to belong to either the supraorbital or infraorbital trunks but to lie in between the two. Free lateralis organs are distributed along the lower edge of the sec- ond and third infraorbital bones, along the pos- terior one-fifth of the lachrymal, and on the membrane of the second pore of the lachrymal (Fig. 17). The ramus buccalis facialis innervates these naked lateralis organs. The ramus buccalis also apparently innervates free lateralis organs medial or dorsal to the anterior and posterior ends of the nasal bone and a patch of these or- gans that lies in skin lateral and ventral to the anterior and posterior narial openings (Figs. 1, 3, and 17). A patch of free lateralis organs in- nervated by the ramus buccalis also occurs on the anterior end of the maxilla, ventral to the anterior nostril. Some branches to canal neuro- masts detach a branch that innervates free lat- eralis organs near an adjacent canal pore. An example is the neuromast branch for the second neuromast and second pore of the lachrymal ca- nal (Fig. 1, I01d2). The ramus buccalis, division IOl of the trun- cus infraorbitalis, forms from the dorsal lateralis root of the facial nerve and moves through the dorsolateral corner of the trigeminal foramen and through the trigemino-facialis complex out- side the foramen. A fairly large contribution of general cutaneous fibers from the Gasserian gan- glion joins it as the ramus buccalis passes ven- 14 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 trally down the lateral side of the trigemino-fa- cialis complex and lateral to the rest of the truncus infraorbitalis. The first branch is IOla (Fig. I) to the lateralis organ in the fourth infraorbital bone (the sixth organ of the infraorbital canal). The ramus buc- calis shortly divides, the larger part remaining as the ramus buccalis, the smaller part, 10 lb, in turn divides into four branches, all being appar- ently the general cutaneous fibers going to skin of the cheek area. The first of these is branch lh (Fig. 1), which passes under the posterodorsal end of the second infraorbital bone and across the cheek underneath skin near the sensory ca- nal of the preopercle. Branch lh turns sharply ventrally and innervates skin in front of and on top of the preopercle about midlength of the ca- nal. Branch lg passes directly posteriorly and crosses the preopercular canal, innervating skin. Branch If is short. It passes under the second infraorbital and ends in skin partway across the cheek towards the preopercle. The fourth branch, le, after contacting a thick branch of I02b from the ramus mandibularis trigeminus (102), passes under the second infraorbital and extends almost in a straight line over to the pre- opercle, where it breaks up in skin overlying the canal of this bone. Branch I02b of the ramus mandibularis trigeminus is mentioned here be- cause it should be part of the ramus buccalis although it detaches from 102, the r. mand. trigeminus. No comparison of this branch was made on other specimens. Branch I02b also passes under the second infraorbital bone about midway along the length of this bone after hav- ing been in contact with branch le of the ramus buccalis. Branch I02b divides into cheek branches lc and Id, both of which pass ventro- posteriorly over the cheek, supplying apparently general cutaneous innervation to skin over to and on top of the preopercular canal. The ramus buccalis next detaches branch IOlc, which shortly divides into IOlcl (Figs. 1 and 3), which supplies the lateralis organ located halfway along the length of the second infraor- bital, and I01c2, which in turn gives off two branches. The first branch, C0R6, innervates conjunctiva and cornea of the posteroventral part of the eyeball and skin connecting the eye- ball and the second infraorbital bone. The rest of I01c2 passes under the second suborbital, emerges at the ventral edge of this bone, rises to skin, and divides into branches 3b and 3c. Branch 3b passes anteriorly, innervating a series of four or five free lateralis organs in a row. It anastomoses with branch 3d. Branch 3c turns posteriorly and innervates a row of four or five lateralis organs along the ventral edge of the an- terior half of the second suborbital bone. The rest of the ramus buccalis continues anteriorly over the floor of the orbital cavity medial to the infraorbital bones and gives off branch IOld, which passes anteriorly giving off branches to the suborbital bones and skin of the cheek. The first branch of IOld (not labeled in Fig. 1) leaves IOld near the anterior end of the second infraor- bital and divides into three branches. Branches la and lb pass ventrally down the cheek, inner- vating skin below the eye and anterior to the preopercular canal. Branches 3d and 3e both supply a row of free lateralis organs lying at the ventral edge of the anterior end of the second infraorbital bone and about three or four organs extending onto the ventral edge of the posterior end of the lachrymal (Fig. 1). Branch 3e is not continuous with branch 3f, although they are shown continuous in Fig. 1. Branch 3d anasto- moses posteriorly with 3b. The last branch of the ramus buccalis to supply free lateralis organs in the infraorbital row is branch 3f, which in- nervates four organs in a row anterior to those innervated by 3e. The four organs lie a little above the ventral edge of the lachrymal bone well posterior to the canal of this bone. The next branch, I01d2. detaching almost at the same point as branch 3f, passes anteriorly some dis- tance and innervates the second lateralis organ in the lachrymal as well as the membrane over the second lachrymal canal pore. The branch innervating the pore membrane detaches from I02d2 inside the lachrymal canal. The next branch of IOld is 3g (Fig. 1). which passes to the exterior of the lachrymal bone and anteriorly some distance, reaching the membrane over the third pore of the lachrymal. Branch 3g inner- vates the patch of free lateralis organs on this membrane. Here is another example of a later- alis branch to a canal organ detaching also a branch to free lateralis organs on the membrane of the adjacent canal pore. The last two branch- es of IOld each innervate a canal neuromast lo- cated near the third lachrymal pore and its mem- brane. After detaching IOld, the ramus buccalis con- tinues anteriorly some distance and divides into IOle and IO If about halfway along the lachry- FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGK1I 15 mal (Fig. 1). Branch 10 le shortly gives off a branch (not labeled) on either side of itself be- fore passing to the first canal organ in the lach- rymal. The first of these branches is a thin nerve that passes anterolaterally medial to the lach- rymal bone. It crosses under the branch to the first lateral line canal organ and emerges from under the lachrymal, where the large articulating surface of the maxilla comes in contact with the anteromedial surface of the lachrymal (Fig. 1). The nerve supplies skin in this area, especially the fold of skin that lies directly ventral to the first indentation on the anterior leading edge of the lachrymal bone adjacent to the articulating head of the maxilla. The second of the two branches of 10 le continues anterodorsally me- dial to the lachrymal and then almost straight dorsally near the posterior edge of the lachrymal where it innervates the skin covering the olfac- tory organ and olfactory chamber. From the ap- pearance of its tiny spraylike endings as seen on Sihler whole-mount nerve preparations, this branch innervates free multicellular sense or- gans located on the skin. The distribution of such organs as seen on serial sections and from whole formalin specimens (Fig. 19) coincides with the location of the spraylike endings just mentioned. The serial sections show the organs to be free lateralis organs. Branch 10 If, which arises at the same point as IOle (Fig. 1), continues anterodorsally, passes ventral to the lateral ethmoid and a little lateral and dorsal to the palatine bone and along the medial wall of the nasal sac. At a point about on the same dorsal level as the first dorsal pore of the lachrymal, 10 If 1 is detached and passes dorsally and then anteriorly medial to the lach- rymal. It apparently innervates only skin on the anterodorsal part of the lachrymal. Branch IOlf continues anterodorsally and divides medial to the first pore of the lachrymal. One of these branches (IOlfa; Fig. 1) passes dorsally, medial to the posterior end of the nasal bone, and in- nervates the membrane over the posterior nasal canal pore and some skin anterior to it. The ter- minal spraylike endings of these branches on Sihler preparations indicate innervation of free multicellular sense organs on the skin. The dis- tribution of free lateralis organs as seen on serial sections coincides with the distribution of the spraylike endings of the nerves. There is little doubt that they are innervating free lateralis or- gans. Branch IOlfb (Fig. 1) continues for a short distance anterodorsally and medial to the lach- rymal before dividing into two branches. One branch passes anterolaterally to innervate skin overlying the dorsal edge of the head of the max- illa and skin ventral to the anterior narial open- ing where there are free lateralis organs (Fig. 19). The other branch passes dorsally up the medial side of the nasal canal and ends in skin medial and dorsal to the anterior end of the nasal canal. There is a patch of free lateralis organs here, which this branch evidently supplies. Ramus maxillaris trigeminus The ramus maxillaris trigeminus of the trun- cus infraorbitalis has two main branches, the ramulus maxillaris superioris to the snout and symphyseal area of the upper jaw and the ram- ulus maxillaris inferioris to the upper jaw. In Polycentrus , at least in the specimen on which the descriptions are based, the superior ramulus is not a separate nerve but courses, to whatever extent it is present, with the ramus buccalis fa- cialis. The inferior ramulus (103; Fig. 1) to the upper jaw is moderately developed. It inner- vates the skin of the premaxilla and maxilla. The following description covers only the inferior ramulus. The ramulus maxillaris inferioris trigeminus leaves the floor of the orbital cavity about half- way across it and passes anterolaterally and ventrally of the palatine bone, then across the lateral side of the palatine but medial to the lach- rymal, giving off as it does two small branches (not shown in Fig. 1) which anastomose with branch IOlf of the ramus buccalis facialis. The next branch, I03a, leaves the inferior ramulus maxillaris and sends a branch to skin on the lachrymal, dorsal to the second and third pores of the lachrymal canal. The remainder of the I03a (Figs. 1 and 16) is branch COR 4, which continues onto the anteroventral quadrant of the eye, innervating skin on the edge of the eye and then the conjunctiva and cornea. The main part of the inferior ramulus (103) continues anteriorly lateral to the palatine and crosses the medial side of the alveolar shaft of the maxilla a little ventral to the curved process of the maxilla in which the premaxillary ascend- ing process rides. As the inferior ramulus (103) leaves the maxilla, it receives the main part of the palatine nerve. The ramulus courses parallel and ventral to the ascending process of the pre- 16 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 maxilla, lying between membranes of the upper jaw (Fig. 1). The external membrane is the skin and the internal membrane is the mucosal lining of the mouth, both having become modified into a stretchable, thin, tough pair of membranes. Before reaching the premaxilla, branch I03b is detached medial to the lachrymal as 103 passes beyond the palatine (Fig. 1). Branch I03b also runs between the jaw membranes, passes lateral to the A, tendon which fastens the cheek mus- cles to the maxilla, and runs close to the dorsal edge of the maxilla towards its distal end. Two- thirds along the maxilla, I03b crosses onto the lateral surface of this bone and shortly divides into three branches. A small branch runs an- terodorsally into the jaw membrane anterior to the maxilla, another ends in skin over the shaft near the distal end of the maxilla, and the main part of I03b continues to the distal end of the maxilla, coursing along the ventral edge of the ligamentous connection between the distal ends of the maxilla and premaxilla. Branch I03b ram- ifies in folds of skin in this region. After passing beyond the maxilla on its way to the premaxilla, 103 receives, as mentioned, the anterior end of the palatine nerve. The juncture of the two nerves varies somewhat on different specimens and on the two sides on the same specimen. On one side, the palatine nerve crosses 103 but then continues alongside it, the two nerves remaining separate for some distance before joining. On the other side, the two nerves remain separate for some distance, except for a small branch, until after 103 bifurcates at two-thirds of the way toward the shaft of the premaxillary bone. The palatine nerve then joins the dorsal fork, I03c (Fig. 1). The dorsal fork and the palatine nerve continue as one nerve towards the base of the ascending process, giving off twigs at right angles, which run in the thin membrane of the upper jaw and innervate it. Just before I03c passes medial to the shaft of the premaxilla, it breaks up into two large and several small nerves. The largest branch I03cl, passes onto the medial side of the premaxilla, penetrates the premaxilla at the edge of the alveolar region, and emerges on its dorsal (external) surface and di- vides, one branch going towards the symphysis of the upper jaw and out onto the lip. The rest of I03cl innervates teeth and lip tissue adjacent to the symphysis. Branch I03cl is the main in- nervation to the lip tissue in front of the sym- physis. The fair-sized remainder of I03c inner- vates the teeth and adjacent tissue of the rest of the premaxillary. It sends a small branch to the premaxillary oral flap and a small branch to the premaxillary membrane (neither branches shown in Fig. 1) and then passes across the medial sur- face of the shaft of the premaxillary until it reaches the alveolar region, where it turns dis- tally and runs in the gum tissue between the middle rows of teeth, supplying the teeth and gums out to the end of the tooth region. The posterior fork, I03d, formed from the bifurcation of 103, slants anteroventrally across the jaw membrane and reaches the lateral sur- face of the premaxilla about one-third of the way along its shaft, giving off en route two branches which supply the area of the lip distal to that supplied by the dorsoanterior fork. The rest of the posterior fork passes in skin diagonally across the premaxilla, giving off branches to the upper lip; leaving the premaxilla one-third of the way from its distal end, it innervates the pos- terior end of the lip. Branch I03d must carry predominantly general cutaneous fibers. Of the three main branches of the compound 103 and palatine nerves, the branch to the alveolar re- gion is the smallest. The conspicuous part of the superior maxil- lary ramulus, the branch to the symphyseal re- gion of the upper jaw that is apparently generally present in many teleosts, is absent in Polycen- trus. The rest of the superior ramulus that in- nervates the skin of the anterior end of the snout no doubt courses as parts of branches IOlfa and IOlfb of the ramus buccalis. Ramus mandibularis trigeminus The ramus mandibularis trigeminus (102) courses for some distance bound to the rest of the truncus infraorbitalis. It leaves the truncus and turns ventrally. Medial to the second in- fraorbital bone, it detaches its first branch, I02a, the ramus opercularis trigeminus (Fig. 1) and continues towards the cheek muscles and the lower jaw. Ramus opercularis trigeminus The ramus opercularis trigeminus, I02a, passes posteriorly towards the hyomandibular, curves dorsally, crosses the anterior edge of this bone a little ventral to its anterior articulating head, continues posteriorly close to the lateral surface of the hyomandibular and divides en route into a dorsal and a ventral branch. The ventral branch breaks up to supply the levator FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII 17 arcus palatini muscle near its insertion. The dor- sal branch passes through this muscle to inner- vate the adjacent dilatator operculi muscle. The main arm of the dorsal branch then innervates the dilatator fibers that pass under the dorsal end of the preopercle (Figs. 1 and 22). After the ramus mandibulars trigeminus (102) has passed ventrally below the second infraor- bital bone, it detaches I02b (Fig. 1 ), a thin nerve that passes laterally across the floor of the or- bital cavity. At the inner edge of the third in- fraorbital, it anastomoses with the anteriormost, fourth branch of IOlb of the ramus buccalis. From the anastomosis three nerves spread out (only 3b and 3c shown in Fig. 1) as they pass under the infraorbital bone and run under skin across the cheek area, as has been described in a preceding section, giving off branches en route and ending in skin covering the preopercular ca- nal. These nerves do not appear to end in the spray typical for branches that innervate free lateralis organs. There are no free lateralis or- gans in this area. These nerves undoubtedly be- long to the general cutaneous system. A second and smaller nerve, not illustrated, detaches at the same place as I02b, diverges anteriorly from I02b, and passes out as another cutaneous branch down the cheek. Innervation of cheek muscle A fair-sized branch, I02c (Fig. 6), passes lat- erally and a little ventrally through the adductor mandibulae muscle mass a short distance below the orbit. The nerve breaks up into a fairly large posterior branch which supplies the ventrolater- al part of the anterior half of muscle A,. How- ever, a sizeable portion (not labeled) of I02c rises to skin not far below the orbit where it divides into numerous branches which pass un- der the third infraorbital to innervate the skin in its vicinity. One rather large branch of I02c curves sharply ventrally (shown in Fig. 6 but not labeled) and passes under the skin of the cheek toward the preopercular canal, giving off what apparently are cutaneous branches to skin. It ends in skin over the anterior end of the pre- opercular canal. The terminal branches in the skin are very fine. The next branch, I02d, arises a short distance further, passes anteriorly, and breaks up in the anterodorsal half of the A, portion of the adduc- tor mandibulae muscle, which it innervates (Fig. 6). A smaller branch of I02d passes posteriorly and shortly divides, the posterior branch sup- plying the more posterolateral part of A,, the anterior branch going to the more ventrolateral part of the anterior half of A,. The fifth branch, I02e, quite large, leaves the ramus mandibularis trigeminus at the same point as does I02d and passes ventroposterioriy (Fig. 6). The first branches to come off I02e ante- riorly form a rather dense ramification on the most medial side of the muscle mass. These branches lie medial to the main trunk of the ra- mus mandibularis trigeminus (102) and appear to supply mainly the muscle fibers which insert by way of the prearticular tendon (TA3; see Fig. 24). Branches from the posterior side of I02e supply the more lateral and ventral fibers of the posterior part of A, in this region, fibers which insert on the ventral end of the maxillary tendon (TA,; see Fig. 24). Most of the rest of I02e passes anteroventrally towards the tendon con- necting the mentalis (Aw) division of the adduc- tor mandibulae, supplying en route the ven- troanterior fibers of this muscle, that is, those which mainly constitute A2. Some of the more dorsolateral muscle fibers which I02e inner- vates insert on the ventral end of the maxillary tendon. After giving off I02d and I02e, the main trunk of 102, the ramus mandibularis trigemin- us, continues anteroventrally, passing between the body of the cheek muscle mass along a rath- er clear-cut separation between what has been designated as divisions A, and A2 of the jaw muscles. As the main ramus reaches the anterior edge of the quadrate a little above its articulating head where 102 is covered laterally by fibers of A2, the nerve forms three large subdivisions. The most ventral of these, the ramulus mandib- ularis cutaneus trigeminus (I02f; see Fig. 6), passes directly anterior to the articulating head of the quadrate onto the lateral surface of the posterior end of the articular bone. Ramulus mandibularis cutaneus trigeminus The first branch detached en route, I02fl, passes medially around the anterior edge of the quadrate. It ends in a dense, localized ramifi- cation of branches (Fig. 10) in the tendinous mucosa which lies on the inside of the mouth directly in front of the anterior edge of the quad- rate near the articulation head of the bone. This tendinous mucosa fans out towards the ventral end of the maxillary tendon. Branch I02fl may innervate stretch receptors located in the jaw OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 membranes in this region. Just before I02f reaches the quadrate, three branches ofI02f are given off. One of these, I02f2, runs dorsally be- neath the skin covering the ventral area of the cheek (Fig. 6; only the stub of this branch is shown) and which fastens onto the articular bone. One twig innervates this skin. A more dor- sal twig innervates the skin area directly poste- rior to the ventral end of the maxillary tendon. A second of the three branches, I02D (Fig. 6; stump only of branch shown), runs beneath skin posteriorly, gives off a small twig to skin lying over the articulating head of the quadrate, and then continues dorsally a short distance, parallel to the ventral edge of the quadrate and bifurcates. One of the two forks extends poste- riorly to the ventral end of the maxillary tendon and ends in very fine branches in the skin near the area supplied by I02fl. The other, larger fork slants posteroventrally over the preoper- cular canal and ends in fine branches in skin directly dorsal to the ventral opening of the pre- opercular canal. It innervates skin close to that innervated by a branch of the ramus mandibu- laris facialis of the truncus hyomandibularis, TH16, but TH16 (Fig. 2) has terminal sprays typical of nerves supplying free lateralis organs in the skin, whereas for the smallest distal branches of the larger fork of I02f3, the termi- nations as viewed on Sihler specimens are very delicate, widely forked twigs and apparently are of the general cutaneous component. The last of the three branches, I02f4 (Fig. 6), passes anteriorly over the lateral side of the pos- terior end of the articular, gives off a small ven- tral branch to skin, then slants dorsally and shortly bifurcates, with fork I02f4b passing close to the dorsal edge of the articular. A short distance up the articular, I02f4b gives off a small branch that enters the fold of bone con- stituting the dorsal edge of the articular. This nerve passes to the end of the dorsal edge and onto the ventral surface of the cartilaginous pad between the posterior end of the alveolar pro- cess of the dentary and the anterior end of the dorsal edge of the articular. It breaks up into tiny branches in this region. The rest of I02f4b continues up the dorsal articular process, de- taches a branch which passes onto the cartilag- inous pad, and then continues in a curved course anteriorly along the ventral edge of the alveolar process of the dentary, gradually becoming smaller. It is apparently a cutaneous nerve. A second branch, which was given off at the same time as this branch from I02f4, also passes to the cartilaginous pad where it could not be fol- lowed. The third branch of I02f4b curves an- terodorsally along the lateral surface of the broad anterior articulating shaft of the articular bone, becomes thinner as it approaches the pos- terior edge of the body of the dentary, and dis- appears between the lateral wall of the dentary and the anterior shaft of the articular. The other fork of the general cutaneous branch of I02f4, branch I02f4a (Fig. 6), extends anteriorly under skin above the articular seg- ment of the mandibular lateral line canal, giving off occasional branches which run downward in the skin over the canal. It becomes progressive- ly smaller until it disappears in skin. Branch I02f4 is apparently all general cutaneous. Shortly after I02f passes onto the articular, it is joined by TH16, a branch from the ramus mandibularis facialis of the truncus hyomandib- ularis. Branch TH16 could be carrying either lateralis or cutaneous fibers or both. Branch I02f from the r. mandibularis trigeminus would be carrying general cutaneous fibers but not mo- tor fibers. Since I02f and TH16 distribute to the same areas and I02f carries only or mostly gen- eral cutaneous innervation, it is not likely that TH16 is carrying this component. More likely, since it detaches from the r. mandibularis exter- nus (Fig. 2) which carries lateralis fibers mainly or only, TH16 must carry lateralis fibers, which it supplies to free lateralis organs of the articular and preopercular areas. The compound nerve (TH16 + IO20, after a short distance, detaches I02f5 (Figs. 6 and 9), which passes postero- ventrally directly ventral to the articulating head of the quadrate. Branch I02f5 shortly sends a small branch which contributes to the innerva- tion of the skin over the posterior opening of the lateral line canal in the articular bone. Branch I02f5 passes medial to the lateral line canal and comes out under skin covering the posterior pro- cess of the articular and angular bones. Here it breaks up into several branches. Branch I02f5a turns anteriorly beneath skin at the postero- ventral surface of the articular, where it disap- pears as fine branches; the other branches come off the remainder of I02f5. Branch I02f5b (Fig. 6) divides into an anterior branch, which passes in skin of the articular ventral to its sensory ca- nal, and into a long, thin posterior branch which runs posteriorly in the ligament connecting the FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII 19 interopercle to the angular and articular. It passes further onto the interopercle, where it anastomoses with a branch from the ramus hy- oideus and gives off en route another branch, I02f5d (Fig. 6), which passes dorsally, medial to the ventral end of the preopercle. Branch I02f5d anastomoses with the r. mandibularis fa- cialis of the truncus hyomandibularis. Branch I02f5e passes posteriorly underneath the ventral edge of the preopercle, giving off branches to skin on the interopercle. A larger branch, I02f5c, continues across the interopercle-artic- ular ligament and onto the ventral skin covering the articulation between the interopercle, artic- ular, and angular bones, and the bases of the anteriormost branchiostegal rays. Branch I02f5 is undoubtedly partly general cutaneous and partly lateralis, since it is a branch of the com- pound nerve formed by TH16 (lateralis) and I02f (general cutaneous). There are free lateralis organs in the area. The remainder of I02f, after detaching the above branches, enters the articular segment of the mandibular lateral line canal and detaches I02f6, a small branch (Fig. 9) which ends in a dense and very finely divided network on the surface of skin covering the articular segment of the mandibular canal. About halfway anteriorly along the articular, the remainder of I02f breaks up into branches I02f7. I02f8, and I02f9. Branch I02f7 (Figs. 6 and 9) passes postero- medially and supplies skin over the medial ven- tral surface of the articular. Two long anterior branches of I02f8 course in skin over the artic- ular and dentary canals. There is a row of free lateralis organs in this skin and a patch of them at the junction of the articular and dentary ca- nals. It could be observed directly that these branches of I02f8 innervated these free lateralis organs. The longer branch of I02f8 ends in skin and membrane around lateral line canal pore number four of the dentary. No free lateralis organs were observed in this area (Fig. 17). The branches of I02f7 and I02f9 ending in skin over the ventral surface of the articular and dentary medial to the lateralis canal apparently are of a general cutaneous component and would be from the r. mandibularis trigeminus, not from the r. mandibularis facialis. The lateralis fibers for I02f8 are apparently all from the r. mandibularis facialis of the truncus hyomandibularis via TH16. which joins I02f above the quadrate's articulating head. Herrick (1899: fig. 3. V-VII.I) found with fairly good certainty such a source of innervation for a small number of free lateralis organs over the canal of the articular bone in Menidia. Returning in the description of the main trunk of the r. mandibularis trigeminus (102) to the point where it detaches I02f (Figs. 7, 9, and 10), it is seen than the ramus mandibularis trigeminus passes anteriorly medial to the muscle fibers that insert on the A2-Aw common tendon, and onto the medial side of the articular, crossing at about midpoint of the posterior edge of this bone. 102 continues anteriorly and a little ventrally on the medial surface of the articular, detaching en route four branches rather close together which innervate subdivisions for the mentalis muscle (Fig. 7). The subdivisions are shown in Figures 23 and 24. Shortly beyond the branches to the mentalis muscle, the r. mandibularis trigeminus (102) detaches the ramulus mandibularis inter- nus trigeminus (I02g; Fig. 7). The remainder of 102 continues anteriorly as the ramulus mandib- ularis externus trigeminus (I02h; Fig. 8). The internal trigeminal ramulus (I02g; Fig. 7) cross- es Meckel's cartilage and runs forward with the ramus mandibularis facialis of the truncus hyo- mandibularis. Branch I02g innervates the pro- tractor hyoidei and intermandibularis muscles, and adjacent skin on the outside, and the mu- cous lining on the inside of the lower jaw. Ramulus mandibularis externus trigeminus After detaching I02g, the ramulus mandibu- laris externus trigeminus (I02h) continues an- teriorly some distance and, near the teeth, it de- taches I02hl (Fig. 10), which carries general cutaneous fibers. I02hl is shortly joined antero- dorsally by TH19a carrying communis fibers. The two branches course together towards the inner edge of the alveolar region of the dentary, where the compound nerve divides. An anterior branch, TH19a4 (Fig. 8), enters the dentary be- neath the inner rows of teeth and courses to- wards the symphysis of the lower jaw, supplying teeth and apparently tissue surrounding the teeth. Two posterior branches run along the in- ner edge of the alveolar region. TH19a3 in bone under the teeth and Thl9a2 next to the alveolar region but in the skin (Fig. 8). The latter nerve breaks up into several parallel branches, one of which, a little posterior to the teeth, drops ven- trally and innervates an area of mucosa lining the inside of the lower jaw. A thin branch. OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 TH19al (Fig. 8), detaches from THl9a shortly after the latter leaves TH19 and runs forward to an area a little posterior and lateral to the sym- physis, where it ends in skin. Shortly before it breaks up, TH19al is joined by a long anterior branch of TH19bl (Fig. 8). Branches of TH19 should be carrying communis fibers for taste buds and mucosa. After detaching I02hl, the remainder of the ramulus mandibularis externus trigeminus (I02h) (Fig. 8) courses anteriorly to near the end of the dentary and detaches a fairly stout branch, I02i, at the curve of the lower jaw. Branch I02i goes to the anterolateral corner of the dentary, near the symphysis, and probably carries mostly general cutaneous fibers. It passes through the dentary directly above the attachment of the la- bial cartilage of the lower lip and directly divides into three large and several small branches which supply the lower lip. The largest of these branches follows the curve of the labial cartilage posteriorly, giving off branches to the posterior half of the lip. One of these branches curves posteriorly across the dorsal surface of the lip and runs in skin of the lip above the teeth of the dentary. Branches pass laterally and anteriorly supplying the anterior half of the lip. After de- taching I02i. the rest of I02h continues ante- riorly as I02j (Fig. 8), which passes under the teeth, has a connection with TH19bl, and, near the symphysis, comes close to and probably joins with the rest of TH19b, which carries com- munis fibers from the r. mandibularis internus facialis. Ramulus mandibularis internus trigeminus Branch I02g (Figs. 7 and 10) of the r. man- dibularis trigeminus (102) remains to be de- scribed. The rest of the r. mandibularis facialis (branches TH19 through TH25) are described in another section along with the rest of the r. man- dibularis facialis and the truncus hyomandibu- laris. The ramulus mandibularis internus trigem- inus (I02g) innervates the protractor hyoidei (geniohyoideus), the intermandibularis muscles, and the skin of the anterior end of the lower jaw in the area of these muscles. It carries a lateralis contribution from the r. mandibularis externus facialis, which innervates free lateralis organs between the anterior ends of the dentary bones. Just before the main trunk of the r. mandibularis trigeminus (102) reaches the dorsal side of Meckel's cartilage, about halfway along the ar- ticular bone, branch I02g is detached. K)2g passes ventrally around the cartilage and comes to lie on the medial surface of the r. mandibularis facialis, runs with it for some distance on the ventral surface of Meckel's cartilage, leaves the r. mandibularis facialis, and continues dorso- anteriorly medial to the cartilage. After branch TH19 is detached (Fig. 10) from the r. mandib- ularis facialis (see section on the truncus hyo- mandibularis for description of TH19), the re- mainder of the r. mandibularis facialis (lateralis fibers from the ramulus mandibularis externus facialis) plus the trigeminal branch I02g (general cutaneous and motor fibers) continue anteriorly medial to Meckel's cartilage. The facial and tri- geminal parts of this nerve cannot be separated. En route to the muscles and skin of the floor of the lower jaw. branches TH20 to TH24 are de- tached. These branches mainly constitute the remainder of the r. mandibularis externus faci- alis, although some cutaneous innervation of the trigeminus courses with them. Only branches I02g2 and I02g2a (Fig. 8), which innervate the protractor hyoidei and the intermandibularis muscles, respectively, and overlying skin are la- beled as deriving from I02g of the r. mandibu- laris trigeminus. Branch I02g2 passes antero- medially (Fig. 8) and detaches I02g2a, which continues anteriorly and is almost contiguous at the midventral line with a similar branch from the opposite side, the two together innervating the intermandibularis muscle (Figs. 8, 9, and 10). The remainder of I02g2 enters the protractor hyoidei muscle, courses posteriorly in it near the medial edge of the muscle, and sends lateral branches into the muscle. Near the point of di- vergence of the two parts of the protractor hyoidei where the belly of each muscle is crossed by a myoseptum, the remainder of branch I02g2 of each side meet. There appears to be some crossing of the nerve fibers of each side over to the opposite side as branch I02g2 continues posteriorly in the protractor hyoidei, I02g2 finally overlapping, as far as could be de- termined; the anterior extent of the ramus hy- oideus passes anteriorly from the hyohyoideus muscle. Ramus Oticus The ramus oticus forms intracranially from a larger bundle of fibers from the dorsal lateralis root and a smaller bundle from the ventral lat- eralis root, both being roots of the facial nerve. FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKU 21 The two bundles join, pass out the lateral side of the trigeminal foramen, and receive general cutaneous fibers from the Gasserian ganglion. The compound nerve passes laterodorsally over the surface of the orbital cavity and into a fo- ramen in the sphenotic bone. En route to this foramen, a branch is detached which innervates the next-to-last lateral line canal organ of the infraorbital series, organ 6. In Figure 1 this branch is labeled 10 la and is shown as detaching from the ramus buccalis facialis. Usually this branch is associated with the ramus oticus (Frei- hofer 1963: fig. 5). A cutaneous branch (not shown in Fig. 1) extends from 10 la underneath the infraorbital bone and ramifies in skin pos- terior to this bone. Upon emergence from the sphenotic bone, the ramus oticus (Fig. 5) lies underneath the last infraorbital bone. It detaches a lateralis branch innervating the single lateralis organ in the last infraorbital, which lies over the sphenotic, and also detaches a branch (not shown in Fig. 1) which passes from under this last infraorbital. It innervates skin overlying the dilator operculi muscle. The rest of the ramus oticus, along with the orbito-pectoral branch of the ramus lateralis accessorius (RLA-OP), which joins it in the porous passageway through the sphenotic, enters a bony passageway at the lateral side of the pterotic canal, shifts medially, and enters the pterotic canal, where it innervates two lateral line canal organs lying close together. The orbito-pectoral branch of the ramus lateralis accessorius continues on and is described in a later section. Ramus Palatinus The ramus palatinus carries communis fibers for the mucosa of the palate and its taste buds, and for taste buds of the upper jaw. The ramus leaves the geniculate ganglion of the facial nerve and passes above the anterior end of the facial foramen. Intracranially the ramus palatinus ap- parently divides into an anterior and a posterior ramus, this division not being discernible on se- rial sections or on Sihler preparations. It may be that both rami arise separately from the genic- ulate ganglion. Two rami are identifiable outside the cranium. The anterior ramus is the main one. The posterior ramus leaves the cranium with the truncus hyomandibularis as branch TH1 (Fig. 4) to the pseudobranch area. The anterior palatine ramus drops sharply ventrally and a little ante- riorly, passing through its foramen in the prootic bone, and enters the prootic chamber connect- ing the trigeminal and facial foramina. It directly enters the wall of the prootic and passes antero- ventrally next to the lateral prootic wall of the posterior myodome chamber. It courses in a bony space outside that of the myodome. Leav- ing the wall of the prootic, it passes through the parasphenoid rather close to the anterior edge of the prootic wing of this bone. It continues next to the top edge of the parasphenoid, grad- ually shifts ventrally, and finally comes to lie alongside the parasphenoid directly above the origin of the adductor arcus palatini muscle. The first branch (not illustrated) passes anterodor- sally in the palatal mucosa, continues halfway anteriorly across the adductor arcus palatini, and curves laterally. It sends several long branches posteriorly that innervate the mucosa of the posterior area of the palate. On the other side of the specimen, a branch was given off from the right anterior palatine ramus that courses near the middle of the parasphenoid bone for about half the length of this bone, and innervates mucosa. The next branch, P2, is giv- en off a little before the main ramus passes an- teriorly beyond the end of the palatal roof (Fig. 4). Branch P2 passes laterally reaching the dor- sal surface of the palatine bone near its anterior end. It detaches en route a branch that courses straight posteriorly some distance, innervating the mucosa of the palate. The rest of P2 bifur- cates at the palatine bone. The anterior fork gives off several twigs; some innervate anterior palatine teeth. One branch continues anteriorly across the ventral surface of the palatine liga- ment connecting the palatine and prevomer and innervates mucosa in this area. Another branch from P2 passes anteriorly across the ventral sur- face of the articulation pad of the maxillary with the prevomer and innervates mucosa in this area. Another branch serves the prevomer area. The posterior, larger fork of P2 courses par- allel and medial to the palatine teeth and gives off a small nerve at the posterior extent of these teeth, the nerve passing anteriorly beneath teeth. The rest of the posterior fork continues onto the ectopterygoid bone, where branches supply mucosa and teeth. Numerous small branches occur in the mucosa medial to the an- terior end of the palatine bone and dorsal to the palatine-prevomer ligament. The rest of the an- terior ramus palatinus, after detaching P2, courses anteriorly, passes beneath the process :: OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 of the maxillary in which the premaxillary spine moves, and continues parallel to the ascending process of the premaxilla and the ramus maxil- laris trigeminus (103; Fig. 1). The anterior pal- atine ramus finally joins the dorsal fork of the ramus maxillaris trigeminus (Fig. 1). On the other side of the specimen, the anterior ramus palatinus joins the maxillary ramus (103) proximal to the splitting of 102 into primary branches to the alveolar region of the premax- illary ramus. Truncus Hyomandibularis All of the nerve fibers and components of the truncus hyomandibularis are derived from the roots of the facial nerve except the general cu- taneous fibers which come from the trigeminal nerve via the ramus communicans and also some sympathetic fibers from the facial sympathetic ganglion. There are four main branches of the truncus hyomandibularis. These are (1) the ramus oper- cularis profundus: (2) the ramus opercularis su- perficialis facialis: (3) the ramus hyoideus: and (4) the ramus mandibularis facialis, which has two main divisions: the ramus mandibularis fa- cialis externus and the r. mand. fac. internus. The ramus opercularis profundus facialis car- ries visceral motor component fibers and inner- vates the muscles of the palate and those moving the hyomandibular bone and opercle. muscles whose origin is medial to these bones. The ramus opercularis superficialis facialis carries lateralis and general cutaneous fibers. In Polycentrus it innervates the dorsalmost two ca- nal organs of the mandibulo-preopercular canal and free lateralis organs on certain scales: one scale near the dorsal end of the preopercle: an- other on the opercle near the operculo-hyoman- dibular articulation: and a third on the anterior end of the side of the subopercle. The ramus hyoideus facialis follows a course mainly along the ventral edge of the hyoid arch, ending a little beyond the anterior end of the arch. In Polycentrus it contains all or nearly all of the general cutaneous fibers that join the trun- cus hyomandibularis from the Gasserian gan- glion of the trigeminal nerve via the ramus com- municans. It also carries visceral motor fibers for the branchiostegal muscles. The ramus hy- oideus apparently carries no lateralis or com- munis fibers. Almost all of the ramus hyoideus innervates the hyoid arch, a small part of it ap- parently continuing into the posterior end of the protractor hyoidei muscle, where it appears to anastomose with a posteriorly coursing branch of the ramus mandibularis trigeminus which in- nervates most of the latter muscle. The ramus mandibularis facialis contains lat- eralis and communis fibers, but apparently none or few general cutaneous fibers and no motor fibers. It has three main branches. One of these is a lateralis branch, the ramus buccalis acces- sorius (TH 10; Fig. 2), which in Polycentrus in- nervates free lateralis organs around some pores of the preopercular canal, a vertical row of free lateralis organs on the cheek in front of the pre- opercular canal, and free lateralis organs along the third and fourth infraorbital bones. Another is the ramus mandibularis facialis externus, which is a lateralis branch that separates from the remainder of the r. mandibularis facialis at the symplectic bone, the remainder of the r. mandibularis facialis at this point being the r. mandibularis facialis internus. These two rami rejoin beyond the symplectic but remain more or less distinct entities, componentwise, but such distinctness is not evident externally. The ramus mandibularis facialis externus is so named because it courses closer to the external surface of the lower jaw, where it supplies lat- eralis organs in the mandibular canal and free lateralis organs in skin on the lower jaw. The last of the three branches is the ramus mandib- ularis facialis internus, which courses separately from the r. mandibularis facialis externus in the region of the symplectic, rejoining the r. man- dibularis facialis externus. in most but not all fishes, medial and anterior to the symplectic. It carries communis fibers for taste buds located mainly at the anterior end of the lower jaw, and those on the lower lip and gum area of the teeth. In Polycentrus there are apparently few or no cutaneous fibers in the r. mandibularis facialis beyond the preopercle. Herrick (1899) found a similar condition for the atherinid Menidia. In the labeling of Figures 2 and 8-13, all of the branches of the truncus hyomandibularis are numbered consecutively, and given the prefix TH, and occasionally a name where one is avail- able. In Polycentrus the ventral lateralis and motor roots of the facial nerve pass through the facial foramen as one combined trunk, the truncus hy- FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII 23 omandibularis (Fig. 31). As the truncus leaves the facial foramen, it receives a bundle of fibers from the facial sympathetic ganglion. Directly after leaving the cranium, a small nerve, TH1 (Fig. 4), the posterior palatine ra- mus, detaches from the truncus and passes an- teriorly and laterally at a level dorsal and ante- rior to the pseudobranch, where it is joined by a nerve of equal size coming from the nervus glossopharyngeus, forming what is called a Ja- cobson's anastomosis. Herrick (1899) used the term ramus pretrematicus facialis for branch TH1 in Menidia but later (1901) changed to the noncommittal term, the posterior palatine ra- mus. The compound facial and glossopharyngeal nerve continues its course through the adductor arcus palatini muscle (Fig. 26) to skin at the pos- terior roof of the mouth in front of the pseudo- branch, where the compound nerve breaks up into five branches. None of these branches was observed to course onto the hyoid arch. Nerve fibers from the glossopharyngeus innervate the pseudobranch (Laurant and Dunel 1966). but no innervation of this organ, a very vascular, gland- like structure in Polycentrus , could be observed by the methods employed. Ramus opercularis profundus facialis The next two branches from the truncus, TH2 and TH3 (Figs. 2 and 4), arise together at the same point from the truncus but course in op- posite directions. Together they constitute the ramus opercularis profundus of the facial nerve. Branch TH2 courses anteriorly through the ad- ductor arcus palatini muscle, innervating it. Branch TH3 (Fig. 4) extends posteriorly medial to the head of the hyomandibular bone. In pass- ing beneath the membrane connecting the pos- terior end of the adductor arcus palatini muscle and the adductor hyomandibularis muscle, TH3 detaches several very small nerves which inner- vate this membrane, which contains only a few muscle fibers (Figs. 4 and 26). It then enters the adductor hyomandibularis muscle near its inser- tion and divides. One division of TH3 gives off three small nerves which run dorsally in the ad- ductor hyomandibularis muscle, innervating it. The other division also contributes to this mus- cle. The two divisions of TH3 are next con- nected by a small branch, and immediately sev- eral rather large branches detach and pass dorsally in the posterior part of the adductor hyomandibularis. The lateral of the two divi- sions of TH3 passes through the middle of the levator opercularis muscle, sending branches in- to this muscle, except for two small branches which join with branches of the vagus coursing down the medial surface of the opercle. One of these vagal branches apparently supplies the an- terior part, and the other the posterior part, of the uppermost portion of the hyoidei adductores muscle. It has not been possible to verify this observation. The lateral division of TH3 cross- es, at right angles, three branches of the vagus and continues into the body of the levator oper- cularis muscle, where it breaks up into a dorsal and a ventral branch of about equal size and a middle, small branch. All run posteriorly in the muscle. No other branches leave the truncus before it passes through its foramen into the hyomandib- ular bone. As it enters this bone, the ramus com- municans from the Gasserian ganglion joins the tr. hyomandibularis on its posterior surface (Fig. 2: r com V). Shortly after entering its canal in the hyoman- dibular and turning ventrally, the tr. hyoman- dibularis detaches the ramus opercularis super- ficialis facialis (Fig. 2; TH4). Ramus opercularis superficialis facialis The ramus opercularis superficialis facialis (Fig. 2; TH4) directly supplies the twelfth, or last, lateral line organ of the mandibulo-pre- opercular canal. The rest of the opercular facial ramus sends a branch which passes directly pos- teriorly and, just in front of the opercle and a little below the operculo-hyomandibular joint, divides into TH4aa and TH4bb. The ventrally directed branch TH4bb passes onto the lateral surface of the opercle a little below the articular head, enters a foramen near the leading edge of the opercle, emerges on its lateral surface, and shortly detaches branch TH4bbl and. a short distance further, branch TH4bb2, which soon rejoin and supply the pocket of a large scale. About 15 free lateralis organs were observed on a scale in this area (Fig. 17). The rest of TH4bb passes ventrally, crosses the anteroventral cor- ner of the opercle, continues onto the suboper- cle a little posterior to the interopercle. and in- nervates free lateralis organs in the skin of this region. There are 15 such organs at this location (Fig. 17). Branch TH4aa passes dorsally. lateral 24 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 to the hyomandibulo-opercular articular head, and ends in skin a little below the point where the preopercular, pterotic, and supratemporal canals open. The terminal twigs of this branch appear the same as those which supply free lat- eralis organs in the skin elsewhere. There are six or more free lateralis organs in this area (Fig. 17). Branch TH4aa apparently supplies these organs. Branch TH5 leaves the hyomandibular, pen- etrates the preopercular lateral line canal, and after a short distance, innervates lateral line ca- nal organ number 1 1 of the mandibulo-preoper- cular canal. A short distance further TH6, a thin branch, detaches and passes posteriorly onto the ante- rior edge of the surface of the opercle that artic- ulates with the preopercle (Fig. 2). Branch TH6 courses down the articulating edge, sending a branch laterally onto the opercle, where it ap- pears to end by several tiny branches in a scale pocket dorsal to the pocket supplied by TH4bb 1 . It does not appear to innervate free lateralis or- gans nor are there any at this location on six whole, formalin-preserved specimens examined. A tiny twig is sent from TH6 into skin over the ligament which connects the preopercle to the interopercle. A small cutaneous branch, TH7 (Fig. 2), was present on one side of the specimen but not the other. About three-fourths of the way toward the articulation of the interhyal with the hyoman- dibular and symplectic bones, the truncus hy- omandibularis detaches TH8, which supplies lateralis organ number 10 of the mandibulo-pre- opercular canal. The truncus next directly gives off the sizeable ramus hyoideus (TH9), which passes down near the posterior edge of the hyoid arch and detaches several cutaneous branches to skin over the anteroventral ends of the oper- cle and subopercle, and the ventral half of the interopercle as well as branches to the hyoidei muscles and to the branchiostegal membrane. The rest of the truncus shortly divides into the rami mandibularis facialis externus and interims. Ramus hyoideus The ramus hyoideus (TH9; Fig. 2) continues ventrally towards the interhyal, but before reaching this bone it leaves the hyomandibular, turns posteroventrally paralleling the interhyal and gives off en route a thin branch, TH9A (Figs. 2 and 13). Branch TH9A crosses the distal end of the interhyal and passes onto the pos- teromedial surface of the epihyal, where it breaks up in the mucous lining of the mouth. The main part of the ramus hyoideus (TH9) passes around the posterior edge of the inter- hyal-epihyal articulation and detaches TH9B (Fig. 2), which passes a short distance to a point above the posterodorsal end of the interopercle, where it divides into TH9B0 and TH9B1 (Fig. 2). Branch TH9B1 goes through the broad liga- ment connecting the interopercle to the shaft of the hyomandibular and shortly divides into four branches, TH9Bla through TH9Bld (Fig. 2), treated together, and into branch TH9Ble. Branch TH9Bla sends long thin branches inner- vating skin covering the joint between the inter- opercle and opercle. Branch TH9Blb courses up the anterior edge of the opercle and anasto- moses with a descending branch of the vagus and with TH6. These branches apparently sup- ply general cutaneous innervation overlying the anterior edge of the opercle. Branch TH9Blc passes to skin covering the joint between the subopercle and the opercle, one small branch ending in this joint. Branch TH9Bld courses posteriorly above and somewhat parallel to the ventral end of the opercle; another branch of TH9Bld passes over the joint and curves pos- teriorly along the ventral edge of the opercle for a short distance, anastomoses with a branch of TH9B02, and detaches several twigs which pass down over the subopercle a short distance, in- nervating skin. The remainder of TH9B1, after detaching branches TH9Bla through TH9Bld, is TH9Ble, which passes along the medial side of the dorsal edge of the interopercle, continues antero ventrally, and turning horizontally, passes medial to the preopercle. About midway across the interopercle, TH9Ble curves ventrally, con- tinues anteroventrally across the medial surface of the interopercle, detaching as it does at least five branches which emerge from under skin on the lateral surface of the interopercle below the preopercle. These branches supply the skin of ten scale pockets on the exposed lateral surface of the interopercle. No free lateralis organs were observed on any of these scales on the six whole specimens examined. The anteriormost terminal branch of TH9Ble anastomoses with a branch from I02f5b (Fig. 2), a general cutaneous branch from the r. mandibularis trigeminus. FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGK1I 25 The details of these branches of TH9B differ on the two sides of the specimen, but the same areas are served by similar branches. Branch TH9B0 arises at the same point as TH9B1. It passes ventrolaterally onto the pos- teromedial surface of the interopercle where it bifurcates. The posteroventral fork. TH9B02, sends a branch to the anterolateral surface of the subopercle where it innervates skin along the ventroanterior half of the medial surface of the subopercle. It does not supply free lateralis organs. Another branch of TH9B02 goes to skin covering the articulating surfaces between the subopercle and interopercle and to skin on the anteromedial surface of the subopercle. Branch TH9B03 runs anteriorly on the medial side of the interopercle and crosses the central area of this bone, where it is joined by a branch from TH9C of the ramus hyoideus (Fig. 13). The com- bined nerve shortly bifurcates: fork TH9B04 continues towards the ventral edge of the inter- opercle, supplying skin medially in this region. It continues anteriorly near the ventral edge of the preopercle and into skin on the ventromedial surface of the posterior end of the lower jaw at the junction of the interopercle, angular, and articular bones. The other fork. TH9B05, runs ventrally close to the ventral edge of the inter- opercle, turns anteriorly and dorsally, and courses beyond the interopercle onto the fold of skin connecting the ventral edge of the lower jaw and the protractor hyoidei muscles, which form, in part, the floor of the mouth. The branch innervates this skin and sends a branch towards the angulo-interopercular joint. Branches TH9B1 and TH9B0 apparently should be assigned to the general cutaneous component. The medial side of the interopercle is supplied mainly by branch TH9B03, whereas the lateral side of the interopercle is supplied mostly by TH9B13. Branch TH9C (Figs. 13 and 2), which leaves the ramus hyoideus (TH9) beyond TH9B, in- nervates the portion of the hyoidei adductores muscle connecting the sixth branchiostegal ray to the opercle (Fig. 13). Immediately after aris- ing, TH9C detaches a thin branch, TH9C1 (Fig. 13), which passes to the medial side of the in- teropercle, where in part it anastomoses with a branch of TH9B0 and then continues as a small nerve which runs forward to the articulating head of the sixth branchiostegal ray and then along this ray innervating apparently muscle and skin in this area. The rest of TH9C supplies the dorsalmost portion of the hyoidei adductores muscle, as already mentioned. A few branches of TH9C cross onto the medial side of the sixth ray and into the muscle spanning the sixth and fifth rays. A few twigs innervate the branchio- stegal membrane spanning the distal ends of the fifth and fourth rays. The remainder of the ramus hyoideus (Figs. 2 and 13) continues anteriorly along the ventral edge of the epihyal and across the medial side of the sixth branchiostegal ray, giving off en route a very thin, long nerve (not shown) which runs posteriorly in the first (dorsalmost) segment of the hyoidei adductores muscle. The tissue was broken in this region, but the nerve appar- ently rejoins the main branch of TH9C. As the ramus hyoideus crosses the sixth ray, another nerve. TH9D (Fig. 13), is given off which passes posteriorly across the sixth, fifth, and fourth rays, decreasing in size as it supplies the muscle and skin connecting these rays. As it crosses the fourth branchiostegal ray (counting the anterior- most ray first), the ramus hyoideus divides into TH9E and TH9F. Branch TH9E passes around the anterior edge of the third branchiostegal ray and into the posterior end of the protractor hyoidei (geniohyoideus) muscle, which it inner- vates, and then anastomoses with the posterior end of branch I02g2 of the ramus mandibularis trigeminus supplying the major part of the pro- tractor hyoidei muscle. A branch (not illustrat- ed) of TH9 in the protractor hyoidei area runs back to the bases of the branchiostegals and ap- pears to innervate the tendons and muscle fibers of the hyohyoidei abductores (H AB: Fig. 25). Branch TH9f supplies the anteriormost segment of the hyoidei abductores (H AB) and the muscle and skin connecting the first and second rays. Small twigs are detached from TH9 as it crosses the fifth to second rays, which innervate the muscle slips of the hyoidei adductores that ori- ginate on the ventral edge of the ceratohyal. Ramus mandibularis facialis The truncus hyomandibularis (Figs. 2 and 13). after detaching TH8 and the ramus hyoideus (TH9), is referred to at this point as the ramus mandibularis facialis. It courses away from the side of the preopercular canal and towards the point where the interhyal articulates with the 26 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 symplectic, passing a little anterior to that point. Shortly it detaches TH10, the ramus buccalis accessorius facialis. Ramus buccalis accessorius facialis The ramus buccalis accessorius (Fig. 2, TH 10) rises through the adductor mandibulae muscle to the skin, where it bifurcates; one fork, (TH10A; Fig. 2), turns dorsally and courses be- neath skin up to the second suborbital bone where, near the posterior end of this bone, TH10A innervates a series of free lateralis or- gans that continues posteriorly near the ventral edge of the third suborbital (Figs. 2 and 17). The other fork, TH10B, runs ventroanteriorly, par- alleling the preopercular canal, and shortly gives off branch TH10B1, a fairly large nerve which passes anterodorsally a short distance and divides into a dorsal and a ventral branch which together course vertically supplying a series of free lat- eralis organs in the skin of two large scale pock- ets. A third scale pocket in the series is supplied by TH10B2, which arises more ventrally from TH10B. The free lateralis organs on these three scales form a vertical row (PCL; Fig. 17). During its course down the preopercle, TH10B has a small connection with the r. mandibulars faci- alis, crosses the anterior arm of the preopercular canal, and detaches TH10B3 and TH10B4. Branch TH10B4 innervates free lateralis organs in the membrane over the pore of the anterior end of the preopercular canal, and branch TH10B3 innervates a cluster of free lateralis or- gans at the second preopercular canal pore. Branch TH10, therefore, supplies apparently only free lateralis organs. These free lateralis organs include those around the second pore of the preopercular canal plus a vertical row of about 20 organs extending dorsally up the cheek area (Fig. 2) and some free lateralis organs ad- jacent to the junction of the second and third suborbital bones. Branch TH10 should be termed the ramus buccalis accessorius. It may be a remnant of the ramus canalis lateralis sys- tem (Freihofer 1972). A similar nerve is present in other percoids. Ramus mandibularis externus facialis and ra- mus mandibularis interims facialis After giving off TH10, the rest of the ramus mandibularis facialis passes directly anterior to the proximal end of the interhyal, at which point it detaches TH11 (Fig. 2), which innervates the fourth canal organ of the preopercle (counting from anteriorly), the ninth organ of the mandib- ulo-preopercular canal. The r. mandibularis fa- cialis next crosses the medial surface of the proximal end of the symplectic and divides into two parts, the r. mandibularis internus facialis and the r. mandibularis externus facialis, the in- ternus portion continuing anteroventrally di- rectly in front of the symplectic and the externus portion passing down the posterior side of the symplectic. The r. mandibularis internus ap- proaches the externus beyond the distal end of the symplectic bone, the two rejoining on the medial surface of the articular head of the quad- rate. Halfway down the quadrate, the r. man- dibularis internus sends a long, thin nerve, TH12a, dorsally up the inner wall of the mouth to the mucosa covering the anterior end of the adductor arcus palatini, where the nerve could not be followed. It presumably innervates taste buds, communis fibers being the main, if not sole, component in the r. mandibularis internus. Further along its course, not far from where it rejoins the r. mandibularis externus, two more thin branches leave the r. mandibularis internus (TH12). One branch (TH12b, not illustrated) is soon joined by another twig also detached from TH12. Branch TH12b passes anteriorly on the medial surface of the quadrate to near the an- terior edge of this bone and then turns dorsally onto the pterygoid bone and passes among the small patch of pterygoid teeth, where it appears to anastomose with a branch of the palatine nerve. Branch TH12c (not illustrated), which arises at the same point as TH12b, passes ven- trally and then laterally around the posterior end of the angular and the articular bones anas- tomoses with the posterior end of I02f (branch I02f5d). Branches very similar to TH12a and TH12B were observed on Sihler preparations of several other percoid fishes. On the opposite side of the specimen, a branch cor- responding to TH12a detaches more proximally along the r. mandibularis internus (TH12) and goes to the same area of skin in the roof of the mouth. Some distance beyond the detachment of TH10, branch TH13 leaves the r. mandibularis facialis at the point of its division into the inter- nal and external facial rami and passes towards the preopercular canal and bifurcates at the edge of the canal (Fig. 2); TH13a sends off one branch which ends in the external skin near the fourth FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGK1I 27 pore of the preopercular canal; another branch passes under the canal and divides, one fork ends in skin at the anterior and posterior sides of the fourth pore of the canal. The other fork, TH13b, courses a short distance anteriorly along the dorsal edge of the horizontal arm of the pre- opercular canal and sends a branch laterally un- der the canal. This branch also splits into two branches under the canal, one branch innervat- ing skin at the anterior side of the third pore of the canal, the other innervating skin of the pos- terior side of this same pore. No free lateralis organs were observed on preserved specimens in the vicinity of the third and fourth pores of the preopercular canal, yet branch TH13b should be suspected of carrying lateralis fibers since the r. mandibularis facialis externus car- ries mainly or only this component. The anterior of the two branches to the third pore sends a branch to skin at the posterior side of the second pore of the preopercular canal. There are free lateralis organs at this pore. TH13 also sends a branch into skin dorsal to the canal. The small remaining part of TH13 anastomoses with TH10. The next two branches, TH14 and TH15, in succession supply sensory canal organs eight and seven of the mandibulo-preopercular canal located between canal pores four and three and canal pores three and two, respectively. A little before the lateralis branch to the first preoper- cular sensory canal organ arises, a fairly large nerve, TH16, comes off the r. mandibularis ex- ternus facialis. TH16 rises to the skin, passes anteroventrally beneath the skin parallel to the posterior edge of the quadrate, and courses around the anterior edge of the articular head of the quadrate, where it anastomoses with I02f of the ramus mandibularis trigeminus (102). The further course of TH16 is described as a part of I02f. TH16 appears to constitute part of I02f5 and apparently carries lateralis fibers, judging from all the other branches of TH10 (the r. buc- calis accessorius). Branch I02f of the r. man- dibularis trigeminus carries only general cuta- neous fibers. The last branch of the r. mandibularis facialis before it is joined by TH12, the r. mandibularis facialis internus, is TH17. a lateralis branch to the first sensory canal organ of the preopercle (Fig. 2). After detaching TH 17, the ramus mandibularis externus facialis contin- ues its anteroventral course, running along the posterior edge of the quadrate bone directly be- neath the mucosal lining of the mouth and di- rectly dorsal to the preopercular canal. The ra- mus mandibularis externus passes over the articular head of the quadrate bone and receives the ramus mandibularis internus (TH12) as it does so. Once again referred to as the r. man- dibularis facialis, the compound nerve passes onto the medial surface of the articular bone; then keeping between the mandibular canal and Meckel's cartilage, the ramus runs beneath mu- cosa for about two-thirds of the way towards the symphysis of the lower jaw, giving off several branches en route (Fig. 10). The first branch, TH17a, innervates the only sensory canal organ of the articular. The r. mandibularis facialis then passes between tendons TA2 and TA, which in- sert the adductor mandibulae muscles on the articular bone (Fig. 24). About halfway between the third and fourth pores of the sensory canal of the dentary, branch TH18 (Fig. 10) passes to the fourth lateralis canal organ of the dentary. A short distance further, the r. mandibularis fa- cialis receives a large nerve, the ramulus man- dibularis externus trigeminus (I02g). from the ramus mandibularis trigeminus (102). Branch I02g, carrying visceral motor and general cu- taneous fibers, courses for some distance with the ramus mandibularis facialis, carrying later- alis and communis fibers, and then a number of branches arise carrying various combinations of these functional components to the anterior end of the lower jaw (Fig. 10). Just before branch TH20 leaves the compound r. mandibularis fa- cialis and I02g, a small nerve, TH18a, appar- ently carrying communis fibers, passes dorsally beneath skin of the medial side of the dentary up towards the posterior extension of the alveo- lar process, where it innervates mucosa in this region. Branch TH20 enters the mandibular ca- nal and innervates the third lateralis organ of the dentary. Before innervating this canal organ, three nerves to the external surface of the den- tary arise from TH20 (Figs. 8-10). The first of these, TH20a (Fig. 8), passes posterolateral^ around the canal, emerges medial to the canal and runs posteriorly beneath skin on the ventral surface of the dentary. It is probably mostly, if not completely, general cutaneous and not lat- eralis in function. Branch TH20b curves antero- lateral^ around the dentary canal and runs an- teriorly and then posteriorly for some distance under skin on the external surface of the den- tary, medial to the canal. It also is apparently a general cutaneous branch. The third branch. OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 TH20c, runs anteriorly on the external surface of the dentary canal almost up to the third pore of the dentary, where it bifurcates; the medial fork passes around the canal and sends one branch anteriorly and another posteriorly. The anterior of these two branches could not be fol- lowed, but the posterior one emerges in skin on the ventral surface of the dentary and runs back medial to the canal. The lateral fork likewise runs posteriorly beneath skin but lateral to the sensory canal. All these branches coming off of TH20 appear to belong to the general cutaneous system. Apparently no free lateralis organs oc- cur in the skin over the dentary canal where these branches terminate. At the point of origin of TH20, the rest of the compound r. mandibularis facialis plus I02g di- vides into two main branches, TH19 and TH21 (Fig. 10). Branch TH19 apparently carries com- munis fibers from the r. mand. internus facialis that supply the taste buds on the lower lip, labial cartilage, and gum area of the teeth as well as other branches to the floor of the anterior end of the mouth. Its branches are described after those of TH21. Branch TH21 (Fig. 10) contains the visceral motor and general cutaneous fibers carried by I02g from the r. mandibularis trigeminus as well as lateralis fibers from the r. mandibularis ex- ternus facialis for the large patch of free lateralis organs near the tip of the lower jaw. It probably carries few or no communis fibers. A number of branches, TH22 to TH25, arise from TH21. Branch TH22, containing mainly the lateralis portion and some general cutaneous fibers of TH21. continues forward along the medial side of the lateral line canal of the dentary and de- taches TH22a to the second canal neuromast of the dentary not far from the symphysis of the lower jaw (Figs. 8-10). The remainder of TH22, after detaching TH22a, continues anteriorly in skin over the ventral surface of the mandibular canal. Halfway towards the second pore of this canal, the remainder of TH22 bifurcates (neither fork illustrated), one fork passing laterally and one medially around the canal, both emerging on the ventral surface of the dentary. The medial fork innervates skin medial to the second pore of the canal. The lateral fork sends a branch anteriorly and one posteriorly, innervating skin lateral to the canal. Branch TH23, the next most medial branch arising from TH21, courses some distance an- teriorly in mucosa covering the dorsal surface of the dentary, penetrates the bone, enters the dentary canal, and innervates the first canal neu- romast of the dentary. Branch TH24 passes an- teriorly until it reaches the medial edge of the dentary, where it detaches two thin branches, one of which, TH24a (Figs. 8 and 9), passes up the inner side of the dentary and innervates skin near the dorsal edge of the first pore at the an- terior end of the mandibular canal. The other thin branch (TH24b: Fig. 9) passes up the ex- ternal surface of the dentary medial to the an- terior end of the canal and innervates skin at the first canal pore. Branch TH24b passes between the medial edge of the dentary and the anterior tendons of the protractor hyoidei (geniohyoid- eus) muscles, reaching skin on the external sur- face of the dentary near the symphysis of the lower jaw below the intermandibularis muscle, where it curves toward the midventral line de- taching small branches to skin between the an- terior ends of the rami of the lower jaw. It then turns posteriorly in skin over the medial edge of the protractor hyoidei and innervates skin. The branches of TH24 going to skin over the anterior end of the dentary canal may be innervating some free lateralis organs. More likely, all the numerous free lateralis organs on the chin be- tween the two dentary rami are supplied by TH25, but this point could not be definitely de- termined. Branch TH25, the next most medial of the branches arising from TH21, passes anterome- dially and continues between the dentary bone and protractor hyoidei muscle of its side, emerges beneath the skin medial to the anterior tendon of this muscle, and ends in branches which appear to innervate numerous free later- alis organs in this area (Figs. 9 and 17). Branch I02g2, which corresponds to branch I02g from the r. mandibularis trigeminus, innervates the intermandibularis and protractor hyoidei mus- cles and overlying skin. It has already been de- scribed under the branches of the r. mandibu- laris trigeminus. Branch TH19 of the r. mandibularis facialis remains to be described (Figs. 8 and 10). It prob- ably contains cutaneous fibers of branch I02g of the r. mandibularis trigeminus, but apparently most of the branches of TH19 are of the com- munis component for taste buds on the lips and the inside of the anterior end of the lower jaw. On Sihler preparations these communis fibers FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKll 29 could be seen to derive from branches of the r. mandibular is facialis internus. Branch TH19 (Fig. 8) continues anteriorly on the ventral sur- face of Meckel's cartilage some distance and divides into branches TH19a and TH19b. Branch TH19a is shortly joined by branch I02h containing apparently general cutaneous fibers from the r. mandibulars trigeminus (102). The two branches course together to the inner edge of the alveolar region of the dentary, where they divide. An anterior branch, TH19a4, enters the dentary beneath the inner rows of teeth and courses anteriorly towards the symphysis of the lower jaw, supplying teeth and tissue surround- ing the teeth. Two posterior branches, TH19a2 and TH19a3 (Fig. 8), course along the inner edge of the alveolar region, branch TH19a2 in bone under the teeth and TH19a3 next to the alveolar region but in mucosa. The latter nerve breaks up into several parallel nerves, one of which, a little posterior to the teeth, drops a little ven- trally and innervates an area of the mucosal lin- ing of the inside of the lower jaw. A thin nerve, TH19al (Fig. 8), detaches from TH19a and courses forward to an area a little posterior and lateral to the symphysis, where it ends in mu- cosa that may contain taste buds. Shortly before it breaks up, TH19al is joined by part of a long anterior branch, TH 19b 1 (Fig. 8). Branch TH 19b departs from TH19a, continues anteriorly me- dial to Meckel's cartilage, and divides into TH19bl and TH19b2. TH19bl passes anteriorly up to the posterior edge of the intermandibularis muscle where it curves medially and connects to I02j and TH19al by a short branch to each one. The rest of TH19bl continues medially into the bone of the alveolar region adjacent to the symphysis and could not be followed. TH19b2 curves medially and detaches TH19b3, a thin, long nerve that arches across the tendon of the protractor hyoidei muscle and runs close to the lateral side of the posterior end of the tendon of the opposite side, where it could not be followed further. A similar nerve from the opposite side comes to lie near it. These branches are appar- ently carrying communis fibers to the floor of the anterior end of the buccal cavity. After de- taching TH19b3, the remainder of TH19b2 passes posteriorly as TH19b4 and innervates the mucosa of the buccal cavity. About halfway along its length TH19bl detaches TH19bla that curves posterolateral^ in the oral membrane of the dentary giving off many fine branches to it. Ramus Lateralis Accessorius The ramus lateralis accessorius (RLA), also referred to as the ramus recurrens facialis or simply the recurrent facial nerve, has been de- scribed in detail for Polycentrus and some other percoids in another paper (Freihofer 1963). Only a summary of its course is given here. The name ramus lateralis accessorius is used in the present paper. The nerve itself has nothing to do with the lateral line innervation. It innervates taste and terminal buds, both of which apparently are basically the same kind of sense organ, the latter being located on the external body surface (Her- rick 1899). The nerve fibers of RLA belong to the communis system of nerve components. The ramus lateralis accessorius in Polycentrus consists of two main branches, an orbito-pec- toral branch (RLA-OP) that courses to the pec- toral, pelvic, and anal fins, and a parieto-dorsal branch (RLA-PD) that courses to the dorsal fin, with some fibers apparently reaching the caudal fin. Both these branches arise intracranially from the geniculate ganglion (Fig. 31). The orbito-pectoral branch (RLA-OP) The orbito-pectoral branch of RLA arises from a sizeable bundle of fibers leaving the an- terior end of the geniculate ganglion anterior to the facial foramen. The bundle passes through the trigeminal foramen and into and through the extracranial trigemino-facialis complex (Frei- hofer 1963: figs. 1-4), and then dorsolateral^ over the posterior wall of the orbital cavity up to and through the sphenotic bone from which it emerges to lie underneath the last infraorbital bone. RLA-OP courses the overall distance in close proximity or contiguous with the ramus oticus. From under the last infraorbital bone, it passes alongside the anterior end of the pterotic canal as far posteriorly as its midlength, where it passes diagonally under this canal over to its medial side and then rises to the overlying skin, at which point it turns posteriorly and pursues a shallow course beneath the skin, continuing either under the ventral end of the supratem- poral canal or between this canal and the pos- terior end of the pterotic canal, then past the dorsal rami of the ramus supratemporalis vagi and the main branches of the nervus linae lat- eralis and onto the medial side of the supra- cleithrum. Crossing this bone, it drops sharply, ventrally down the medial side of the cleithrum onto the first postcleithrum, then alongside the JO OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 posterior edge of the second postcleithrum, and continues more or less diagonally under skin to near the midventral line, reaching it just poste- rior to the anus. From this point posteriorly, it courses next to the bases of the anal spines, ap- parently supplying communis fibers to each branch of a segmental ventral spinal ramus that enters an anal spine or ray. In its course past the pectoral fin, RLA-OP detaches branches which innervate the pectoral fin (for details see Freihofer 1963). A branch is detached to the pelvic fin as RLA-OP passes this fin. The parieto-dorsal branch (RLA-PD) The parieto-dorsal branch of the ramus later- alis accessorius arises by two roots from the large geniculate ganglion which separately pass dorsally around the overlying dorsal lateralis root of the facial nerve and join above it (Fig. 31). RLA-PD passes laterally over to the inside of the cranial wall, encounters the radix profun- dus and its ganglion, or nearly does, and then rises to the cranial roof beneath the parietal bone, where it is met by the intracranial dorsal vagal ramus, which was identified on serial sec- tions as belonging to the rami cutanei dorsales vagi. This vagal ramus did not actually contact RLA-PD in two Sihler preparations examined but was seen to remain separate from it and to pass anteriorly a short distance to innervate skin. It was sometimes observed on Sihler nerve preparations of several kinds of fishes not to join with RLA-PD nor course with the latter nerve. It seems unlikely that this vagal ramus carries communis fibers as maintained by Her- rick (1899). After passing through the parietal bone, RLA- PD continues laterally across the parietal ridge and to the overlying skin and then posteriorly towards the middorsal line and the dorsal fin. It has similar relations to branches of the dorsal spinal rami innervating the fin spines, rays, and membrane that RLA-OP does for the anal fin. None of the branches of the ramus supratem- poralis vagi fuse with RLA-PD as Herrick ( 1899) found in the atherinid Menidia. It could not be determined by the methods used in this study whether or not any taste buds were innervated by the two main branches of RLA between their cranial exit and the fins or whether there are taste buds in these areas. Innervation of the Gill Arches There are four filament-bearing gill arches in Polycentrus (Fig. 18, CB1-CB4) and a fifth gill arch which bears no gill filaments and has only one bone supporting it, the fifth ceratobranchial (Fig. 18, CB5). Each of the first four arches has two vertical rows, a medial and a lateral, of gill filaments and a lateral and medial row of gill rakers (Fig. 20, LGR, MGR). Two pairs of cranial nerves, the glossopha- ryngeus (IX) and the vagus (X), innervate the five arches and their associated muscles (Fig. 19). The second or third gill arch exhibits the more complete pattern of branching of a branchial nerve trunk to its gill arch. Typically a branchial nerve trunk divides into two rami, a pretrematic and a posttrematic. The pretrematic ramus of a branchial nerve trunk passes down its gill arch anterior to its gill slit; the posttrematic ramus passes down the succeeding gill arch lying pos- terior to the same gill slit. For the third gill arch, its pretrematic branchial ramus (Fig. 19, V2PR) innervates the area of the medial row of gill fil- aments, and its posttrematic ramus (Fig. 19, V2PO) innervates the lateral row of gill filaments of the next posterior gill arch. The glossopha- ryngeus nerve innervating the first gill arch has a posttrematic ramus (Fig. 19, GLR) passing down the first arch, but the pretrematic ramus (G2) for the glossopharyngeal nerve courses an- teriorly onto the palate, where it joins the pos- terior ramus palatinus. The medial side of the first gill arch and the whole second, third, and fourth gill arches are innervated by vagal bran- chial trunks one, two, and three, each of which has a pretrematic and posttrematic ramus (see symbols for each arch. Fig. 19). After passing onto a gill arch, posttrematic rami 2, 3, and 4 each gives off a small nerve (shown diagram- matically large in Fig. 19) that passes down the anterior face of a ceratobranchial bone, coursing between the lateral and medial rows of gill rak- ers, innervating these rakers and the mucous epithelium between them. It is referred to as the gill raker ramus (G6, V1B, V2F). It apparently does not innervate gill filaments. The pretrem- atic ramus of each branchial arch nerve trunk also has a pharyngeal ramus. Other branches of the pretrematic or posttrematic rami innervate the various gill arch muscles and mucous epi- thelium on the floor of the gill arches. In Poly- FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII 31 centrus one gill arch muscle, the protractalis pectoralis, is innervated by a branch that comes from the ramus supratemporalis vagi (Fig. 19, PRPE). Branches to the muscles of the gill arch- es and gill filaments detach from the posttrem- atic, not from the pretrematic rami. Nervus Glossopharyngeus The glossopharyngeal, or ninth pair of cranial nerves, arises by a single root on each side a little below the midlateral extent of the medulla and courses posteroventrally a rather short dis- tance to its cranial exit in the exoccipital bone at the posterodorsal end of the swelling of the otic bulla (Figs. 26, 29). The glossopharyngeal foramen lies directly in front of the vagal fora- men but separated fiom the latter. Shortly be- yond its cranial exit, the glossopharyngeus is joined on its ventral surface by the sympathetic trunk. The two course closely bound together an- teriorly three-quarters of the way across the otic bulla at which point the petrosal ganglion forms on the glossopharyngeus. A little before or after the petrosal ganglion, some ganglion cells form in what must be the sympathetic part of the com- pound nerve. The two nerves then separate, the glossopharyngeus continuing anteriorly. At the anterior end of the otic bulla it detaches branch Gl (Fig. 19), which passes anterolaterally and innervates the levator internus II branchial mus- cle (Fig. 18, LI2). On some Sihler nerve prepa- rations, the glossopharyngeus itself passes through this muscle as it innervates it. The glos- sopharyngeus next detaches branch G2, the ra- mus pretrematicus IX, which passes anteriorly and then medially. Upon reaching the proximal head of the first, or suspensory infrapharyngo- branchial bone, G2 meets the posterior palatine ramus (PPR, Fig. 19; TH 1 . Fig. 4) from the trun- cus hyomandibularis. These two nerves join forming Jacobson's anastomosis, then course anteriorly past the pseudobranch and innervate skin over the posterior end of the palate in the vicinity of the pseudobranch, which is a highly vascularized saclike structure in Polycentrus. The glossopharyngeus, in turning laterally, crosses the anterolateral surface of the levator internus II (LI2; Fig. 18) and passes around the medial and anteroventral surface of the levator externus I (LEI) branchial muscle which it in- nervates by branch G3 (Fig. 19). The glossopha- ryngeus (IX; Fig. 19) continues onto the dorsal surface of the first epibranchial bone (EP1; Fig. 18) and laterally along this bone, lying under the bases of a lateral row of gill filaments, this part of the glossopharyngeus being the posttrematic branchial ramus (GLR) of the first gill slit. It continues ventrally onto the ceratobranchial along its posterolateral side under the lateral row of gill filaments. Halfway down the first cera- tobranchial, the posttrematic ramus (GLR) de- taches a small gill raker branch that passes an- teriorly a short distance and which, upon reaching the anterior face of the first gill arch, is joined by a similar gill raker branch (not la- beled on Fig. 19) from the pretrematic first vagal branch (not labeled) from the pretrematic first vagal branchial ramus (VI PR). The joined branches (G6; Figs. 19, 20) pass ventrally be- tween the lateral and medial rows of gill rakers innervating them. As the posttrematic ramus of the glossopharyngeus (GLR; Fig. 19) proceeds down the posterolateral side of the ceratobran- chial along the bases of the lateral row of gill filaments, a series of very small branches are sequentially detached, each of which passes posteriorly and join together forming a vertical branch, G5 (Fig. 20). Branch G5 weaves in and out between the gill filaments, apparently sup- plying the muscles of the filaments. The posttrematic of the glossopharyngeus (GLR) detaches branch G7 (Fig. 19) near the ventral end of the first ceratobranchial: G7 in- nervates the obliquus ventralis I (OV1) muscle (Fig. 18). The remainder of the posttrematic (GLR, Fig. 19), continues down the lateral face of the first hypobranchial bone and ventrally around its anterior end and up medially and an- teriorly to the side of the basihyal bone, along which it courses anteriorly innervating mucosa at the side of the tongue lateral to the basihyal. En route past the first hypobranchial, the glos- sopharyngeus detaches branch G8 (Fig. 19) for the rectus ventralis I muscle (RV1, Fig. 18). A branch is given off for the mucosa on the floor of the mouth dorsal to the first basibranchial and dorsal hypohyal. The last branch given off runs posterolaterally on the dorsal surface of the dor- sal hypohyal towards the first ceratohyal. Nervus Vagus The functional components of the nervus va- gus, or tenth pair of cranial nerves are (1) vis- ceromotor and communis fibers contained in the 32 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES. NO. 128 pharyngobranchial and intestinal rami: (2) gen- eral cutaneous and possibly communis fibers in the rami cutanei dorsales vagi: general cuta- neous fibers in the opercular ramus: lateralis and general cutaneous fibers in the supratemporal ramus: and (3) visceromotor fibers in the cardiac ramus. The intestinal and cardiac rami are not considered further. The lateral line nerve of the trunk of the body is considered separately from the vagus. Herrick (1899) found the general cu- taneous component to be very small in the vagus of the atherinid Menidia, but he found the motor component to be of considerable size, with the communis component by far the largest. Similar relative developments exist in the percoid Poly- centrus. The cell bodies for the general cuta- neous component are located in the jugular gan- glion of the vagal nerve: neither this ganglion nor its root was distinguishable from the rest of the ganglion and common root of the vagal nerve in Polycentrus . According to Herrick (1899). fibers of the communis system are of two kinds: fibers that innervate taste buds and fibers that innervate general visceral and mucous surfaces by the simplest free nerve endings. The latter would be comparable to the general cutaneous fibers of external body surfaces. The root of the vagus arises from the midlat- eral side of the medulla by four rootlets on dis- sected specimens, but these appear very close together on serially sectioned specimens and are not distinguishable. The vagal root passes a short distance posteroventrally to its foramen in the exoccipital bone, the foramen for the glos- sopharyngeal nerve lying a short distance ante- rior to that for the vagus (Figs. 4, 25. 28-30). Intracranially the nervus vagus is separate from the nervus linae lateralis (NLL). The two nerves pass through the same foramen together, the nervus linae lateralis a little anterior and medial to the nervus vagus. Intracranial dorsal vagal ramus Two-thirds along its intracranial course, the nervus vagus detaches a fairly large ramus. This vagal ramus may be equivalent in part to the rami cutanei dorsales vagi of Menidia, which rami Herrick (1899) found to arise from the jug- ular ganglion outside the cranium, not inside as in Polycentrus . Part of the rami cutanei dorsales vagi of Polycentrus does pass out the cranium as in Menidia through the vagal foramen. The intracranial vagal ramus in Polycentrus passes dorsally a short distance from the root of the nervus vagus and detaches a branch about one-third its own size, the extracranial vagal ra- mus, which passes towards the vagal foramen in the exoccipital bone where the extracranial vagal ramus forms a ganglion just before reach- ing the foramen. This ganglion is the jugular gan- glion of the vagal nerve, the ganglion for general cutaneous sensory neurons. The extracranial vagal ramus (the rami cutanei dorsales vagi, in part) passes through the dorsolateral corner of the vagal foramen between the nervus linae lat- eralis and the slightly posterior root of the ner- vus vagus. The extracranial vagal ramus was traced on serial sections almost up to three size- able fiber bundles lying lateral to the nervus lin- ae lateralis as this nerve leaves the cranium. The extracranial vagal ramus could not be traced be- yond this point. The extracranial vagal ramus evidently joins with the three groups of fibers which are evidently lateralis, and together form the ramus supratemporalis vagi. More ganglion cells form in the supratemporal ramus as it moves laterodorsally and anteriorly away from the nervus linae lateralis. The further course of the ramus supratemporalis vagi is described af- ter the intracranial vagal ramus. One of the three fiber bundles forming the ra- mus supratemporalis vagi, or part of one of these bundles, must be of motor fibers for the pro- tractalis pectoralis muscle. Another of the bun- dles is of lateralis fibers for the posttemporal and supratemporal canals. The fiber bundle from the intracranial vagal ramus must be carrying gen- eral cutaneous fibers and possibly communis fi- bers for taste buds, but the methods used in the present study did not permit definite determi- nation of the presence or absence of communis fibers in any of these rami. Shortly after the intracranial dorsal vagal ra- mus detaches the extracranial ramus that evi- dently joins the ramus supratemporalis vagi, the intracranial division forms a sizeable ganglion. The ramus then rises dorsoanteriorly and me- dially in the cranial cavity up to the parietal bone, through which it passes close to the exit of the ramus lateralis accessorius (RLA-PD) but medial to RLA and about on the same transverse plane with it. Before reaching the parietal, the intracranial dorsal vagal ramus bifurcates. Both branches exit through the parietal, pass trans- versely across the parietal ridge, and innervate FREIHOFER: CRANIAL NERVES OF POLYCESTRUS SCHOMBURGKU 33 skin on the side of the head dorsal to this ridge. The intracranial vagal ramus exiting through the parietal is missing in Menidia (Herrick 1899). It is absent in the atherinid Atherinops affinis (Freihofer 1963). It seems most probable that this intracranial vagal ramus is not carrying communis innerva- tion for taste buds, since RLA which does carry such innervation passes through or close to the area on top of the head served by the intracranial vagal ramus. Nor would it likely be carrying lat- eralis fibers, since the r. supratemporalis vagi, which carries lateralis fibers, innervates the ad- jacent area posteriorly, and SORB2 of the su- praorbital trunk, also carrying lateralis fibers, innervates the adjacent area anteriorly. If the foregoing statements are correct and the intra- cranial vagal ramus carries neither lateralis nor communis fibers to the skin, the ramus must be carrying general cutaneous fibers. Rami cutanei dorsales vagi The rami cutanei dorsales vagi comprise the general cutaneous bundles of fibers coursing with the nervus vagus (Herrick 1899). Branch r. supr. 2a in Polycentrus (Fig. 5) is apparently a cutaneous dorsal branch of the supratemporal vagal ramus and belongs to the rami cutanei dor- sales vagi system, but it is described in Poly- centrus under the ramus supratemporalis vagi. The intracranial dorsal vagal ramus described above also apparently belongs to the general cu- taneous system of branches comprising the rami cutanei dorsales vagi. Although described in Polycentrus as a separate ramus, the ramus opercularis vagi (Figs. 11-12. and 19) is appar- ently general cutaneous in function and also be- longs to the rami cutanei dorsales vagi. Ramus opercularis vagi The ramus opercularis vagi is associated prox- imally with the ramus supratemporalis vagi (Fig. 12). In Polycentrus the ramus opercularis vagi arises from a thin, elongate ganglion lying out- side the cranium and beneath the nervus linae lateralis as this nerve leaves the vagal foramen. The cutaneous root from which the ganglion came could not be observed as a separate entity. Herrick (1899) assigns the r. opercularis vagi to the rami cutanei dorsales vagi. As seen on serial sections, the ramus opercularis vagi is a rather independent entity, although it lies in close proximity to the basal part of both the nervus linae lateralis and the ramus supratemporalis vagi (Fig. 12). The ramus opercularis vagi leaves the side of the ramus supratemporalis vagi near the origin of the latter from the nervus linae lat- eralis (Fig. 12) and detaches its first branch (PRPE: Fig. 12). which is a visceromotor nerve innervating the nearby protractalis pectoralis muscle lying dorsal to the fourth gill arch. This motor branch is not considered part of. but only associated with, the rami cutanei dorsales vagi. The temporal branch (r. supr. 2a) of the r. su- pratemporalis vagi may come off as part of the ramus opercularis vagi (Fig. 5) or as a separate branch from the ramus supratemporalis vagi, detaching before the ramus opercularis vagi. The ramus opercularis vagi passes dorsally above the adductor opercularis muscle, across the tip of this muscle, and down its lateral side to the dorsal edge of the opercle. where it pen- etrates the opercle a little posterior to the hy- omandibulo-opercular articulation at about the level of the horizontal thickening of the bone right at the line of insertion of the adductor oper- culi muscle. Here it divides into three branches, r. op. 1-3 (Fig. 12). Branch r. op. 1 appears to go to the mucosa covering the dorsoposterior side of the posterior wall of the last gill slit. Branch r. op. 2 passes to skin dorsal to the oper- cle and gives off branch r. op. 2a. which comes close to the terminations of branch TH4AA of the truncus hyomandibularis in the area where a large scale bears a row of free lateralis organs (Fig. 2). These lateralis organs are innervated by TH4AA. not by a branch of r. op. 2a. The rest of r. op. 2a innervates skin on the dorsoposterior lateral side of the opercle (Fig. 11). Branch r. op. 3 innervates most of the medial surface of the opercle down to the subopercle (Fig. 12). where it anastomoses with dorsally coursing branches of TH9C (from the ramus hyoideus) that terminate in the branchiostegal membrane. One dorsal branch of r. op. 3 passes posteriorly and innervates the opercular membrane both dorsal and ventral to the opercular spine. Branch r. op. 3 is the only branch found to ex- tend below the opercle any distance. Where it does extend below the opercle, it enters the branchiostegal membrane and does not appear to course on the subopercle. The innervation to the subopercle is, in part, by several fine branch- es coming down from a branch of the ramus opercularis vagi that extends horizontally along the line of contact between the opercle and sub- opercle (Fig. 12) and. in part, by fine branches 34 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 from the ramus hyoideus coming onto it at the anterior end of the gill cover (Fig. 2). Ramus supratemporalis vagi The ramus supratemporalis vagi (Fig. 5) con- sists mainly of lateralis fibers from the root of the nervus linae lateralis and, to a small extent, of general cutaneous fibers. Most of the cuta- neous fibers are apparently carried in branch r. supr. 2a (described below) and also in branch r. supr. lb (Fig. 5). Communis rami detaching from the r. supratemporalis vagi and from the ante- riormost branches of the nervus linae lateralis were observed by Herrick (1899: fig. 3; a. r. VII. 1, 2, and 3) to join the ramus lateralis ac- cessorius (RLA) extracranial^ on the top of the head and nape. No such communis rami were identifiable in Polycentrus . The components for the r. supratemporalis vagi in Polycentrus are apparently only lateralis and general cutaneous (see also under section on rami cutanei dorsales vagi). Herrick may be wrong in his interpreta- tion of the three rami in Menidia. As the r. supratemporalis vagi and nervus lin- ae lateralis move away from each another, a ganglion forms in the ventral part of the r. su- pratemporalis vagi, and the ramus shortly di- vides into two main branches: branch r. supr. 1, carrying mainly lateralis fibers innervating lat- eralis organs in the posttemporal and supratem- poral canals, and free lateralis organs in a ver- tical row of scales above the supratemporal canal, but carrying also some cutaneous fibers for skin dorsal to these canals (Fig. 5); and branch r. supr. 2, carrying lateralis fibers to free lateralis organs in a vertical row anterior to the supratemporal canal (STL; Fig. 17) as well as some cutaneous fibers to skin of the temporal region (Fig. 5). Branch r. supr. 1, after separating from r. supr. 2, passes straight laterally across the base of the cranium and swings dorsally medial to the cranio-pectoral-girdle muscle, the levator pectoralis, and continues dorsally medial to the supratemporal canal, where it detaches branch r. supr. la, which innervates the lateralis organ in the posttemporal canal. From branch r. supr. la, a branch passes ventrally (shown extending horizontally in Fig. 7) below the posttemporal canal, where it shortly breaks up in thick skin in front of the dorsal end of the supracleithrum. Also detached medially of the supratemporal canal is r. supr. lb. It innervates skin located between the anterior, epiotic arm of the post- temporal bone and the posterior end of the su- pratemporal. The rest of r. supr. 1 detaches r. supr. lc and r. supr. Id, each of which inner- vates a lateralis canal organ in the supratemporal canal. Branch r. supr. 1 then continues in a dor- soanterior curve towards the middorsal line, in- nervating three scales, each of which bears a row of free lateralis organs that together form a continuous, almost vertical line of organs (Fig. 17). Branch r. supr. 2a (Fig. 5) is apparently a gen- eral cutaneous branch and belongs to the system of branches that Herrick (1899) calls the rami cutanei dorsales vagi. R. supr. 2a passes dor- sally medial to the posterior end of the pterotic canal and medial to the anteroventral end of the supratemporal canal where it turns anteriorly, coursing under and innervating skin on the side of the head dorsal to the pterotic in the temporal area of the head. The remainder of r. supr. 2 continues dorsally and detaches another branch that courses towards the temporal area but passes lateral to the levator pectoralis muscle that extends from the posterolateral corner of the cranium back to the proximal end of the op- isthotic arm of the posttemporal bone. Branch r. supr. 2 curves dorsoposteriorly and innervates the long vertical row (Fig. 17, STL) of free lat- eralis organs lying across three consecutive scales anterior to the supratemporal canal. En route r. supr. 2 crosses the orbito-pectoral branch of the ramus lateralis accessorius and runs a short distance anteriorly along RLA-OP. First vagal branchial trunk The first vagal branchial trunk, VI, for the second gill arch detaches itself from the pha- ryngo-intestinal trunk of the vagus (Fig. 19; see symbols for each branchial trunk) shortly after the latter leaves the cranium at the anterior end of the head kidney. It continues anteriorly and then anterolaterally and ventrally, passing me- dial to the internal and external levator branchial muscles. Medial to these muscles the first vagal branchial trunk detaches VIA (Fig. 19), which innervates the levator externus II muscle (LE2; Fig. 18). Before the detachment of VIA, a gan- glion forms on the first branchial trunk. A short distance further, it detaches a second branch (not shown in Fig. 19) to the levator externus II muscle. Before passing around the second le- vator internus branchial muscle, the first vagal FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII 35 branchial trunk (VI) divides into pretrematic (V1PR) and posttrematic (V1PO) rami. The pre- trematic ramus (V1PR) to the first gill arch shortly detaches a pharyngeal ramus, VIP, which passes ventrally directly posterior to the cartilaginous medial process of the first epibran- chial bone and continues medially, reaching the mucous epithelium anterior to the second infra- pharyngobranchial bone. Continuing antero- ventrally from near the base of the pharyngeal ramus (VIP) is branch VIE, here referred to as a gill raker ramus. Branch VIE passes onto the ventral surface of the first epibranchial where it turns posteroventrally between the two rows of gill rakers. Branch VIE meets a second gill raker branch from the first vagal pretrematic ramus at the junction of the first epibranchial and cera- tobranchial bones. The reenforced gill raker ra- mus continues ventrally between the two rows of gill rakers. The remainder, and larger part, of the first pretrematic vagal branchial ramus (V1PR), passes onto the posteromedial side of the first epibranchial bone at the upper end of the medial row of gill filaments and continues ventrally un- derneath the filaments, following them onto the ceratobranchial. The first pretrematic ramus de- taches the second gill raker branch (described above) at the junction of the epibranchial and ceratobranchial bones of the first gill arch. This ramus passes around the ceratobranchial to its anterior surface and continues in the mucous epithelium between the lateral and medial rows of gill rakers, innervating them and the epithe- lium to its junction with a similar gill raker branch from the posttrematic ninth nerve (GLR: Fig. 19). The latter branch continues ventrally to the end of the gill raker rows on the first hy- pobranchial bone. The remainder of the first va- gal branchial pretrematic ramus continues under the medial row of gill filaments to its termination on the first hypobranchial. The posttrematic ramus (V1PO) continues on- to the second gill arch, passing onto the pos- terolateral surface of the second epibranchial bone and underneath the lateral row of gill fila- ments, and then onto the second ceratobranchial bone where it continues underneath the postero- lateral row of gill filaments to the end of the second ceratobranchial. At the junction of the second epi- and ceratobranchials, the posttrem- atic branch (V1PO) detaches a gill raker branch which passes around to the anterior surface of the second ceratobranchial, down which it con- tinues between the two rows of gill rakers to the end of the second ceratobranchial. The last im- portant branch of the posttrematic ramus is branch VIC, which innervates the obliquus ven- tralis II (OV2) branchial muscle (Fig. 18). The posttrematic ramus (V1PO) ends after passing between the second cerato- and hypobranchials where it innervates mucous epithelium at the base of the gill arch. Second vagal branchial trunk After giving off the first vagal branchial trunk, the rest of the vagus, consisting of the remaining branchial trunks and the ramus intestinalis, passes ventrally and gives off the second vagal branchial trunk which innervates the third gill arch. This trunk passes laterally a short distance and forms the second vagal branchial ganglion. From this ganglion (Fig. 19), the pretrematic and posttrematic rami (V2PR and V2PO) arise and parallel each other for some distance anteriorly. En route to the second gill arch, the second va- gal pretrematic ramus (V2PR) detaches the pha- ryngeal ramus, V2P, which passes medially be- tween the second and third pharyngeal bones, innervating the mucous epithelium and teeth. The rest of the pharyngeal ramus (now labeled V2E) continues as the upper gill raker ramus for the second gill arch onto the anterior surface of the second epibranchial and ventrally down it between the two rows of gill rakers. It then joins the gill raker branch (V1B) from the posttrem- atic of the first vagal ramus and continues onto the anterior surface of the second ceratobran- chial, innervating the two rows of gill rakers and the intervening mucosa. The rest of the second pretrematic ramus (V2PR) passes onto the pos- teromedial surface of the second epibranchial underneath the medial row of gill filaments, in- nervating them to the end of the second cera- tobranchial. Just beyond the second smaller ganglion of the second vagal pretrematic ramus, there are two short connections between the two main ra- mi of the second vagal branchial ramus. At the first of these two connections, branch V2A leaves the posttrematic second vagal branchial ramus (V2PO), passes laterally and innervates the levator posterior branchial muscle (LEP). Closely thereafter a larger branch, V2B, detach- es from the posttrematic and passes anterolater- ally and innervates the large levator externus IV 56 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 (LE4) branchial muscle. At the site of the two cross connections, or independently of them and from the second pretrematic branchial ramus, branch V2C detaches and passes anteriorly be- tween the pretrematic and posttrematic second vagal rami. It continues parallel to the latter and above the obliquus dorsalis III muscle (OBD3), detaches a branch (not labeled on Fig. 19) that innervates this muscle and another branch, V2D, that passes anteriorly and innervates the transversus dorsalis II (TD2) branchial muscle. The second posttrematic vagal ramus (V2PO) continues anteroventrally medial to the large le- vator externus IV branchial muscle (LE4) and dorsal to the obliquus dorsalis III muscle (OBD3). Then it passes onto the dorsal surface of the third epibranchial and underneath the dor- sal end of the lateroposterior row of gill fila- ments of the third arch and continues under- neath the row of filaments to its end at the base of the third ceratobranchial bone. A gill raker branch (V2F) is detached at the joint between the second epi- and ceratobranchials and passes around the arch to its anterior surface where it meets a more dorsal gill raker branch (V3E) from the pretrematic ramus of the fourth vagal branchial trunk. Branch V2F passes ventrally between the two rows of gill rakers, innervating them and intervening mucous epithelium to the end of the third ceratobranchial. The remainder of the posttrematic ramus (V2PO) of the second vagal branchial trunk, af- ter giving off branch V2F, continues down the third ceratobranchial at its lateroposterior side beneath the bases of the lateral gill filaments to the end of the row. At the base of the third cer- atobranchial, the remainder of the posttrematic ramus gives off branches innervating four ven- tral branchial muscles and then ends in mucous epithelium overlying the hypobranchial and ba- sibranchials of the third arch. The four branches are branch V2J to the third obliquus ventralis muscle (OV3); branch V2H to the rectus ven- tralis IV (RV4) muscle; a large branch, V2G, to the rectus communis (RCOM) muscle; and a branch (not shown in Fig. 19) to the rectus ven- tralis V (RV5) muscle. Third vagal branchial trunk The third vagal branchial trunk for the fourth gill arch separates proximally from the second vagal branchial trunk, forms a ganglion, passes ventrally a short distance, and detaches branch V3A which drops ventroposteriorly and inner- vates the retractor dorsalis (RETD) muscle, en- tering this long muscle anteriorly near its at- tachment to the third infrapharyngobranchial bone. Next, the third vagal branchial trunk di- vides into the pretrematic (V3PR) and posttrem- atic (V3PO) rami, which continue close together anteroventrally towards the fourth epibranchial. The pretrematic ramus (V3PR) passes medial to the levator externus IV muscle (LE4), crosses the dorsal surface of the fourth and third epi- branchials, and detaches the pharyngeal ramus, V3P. The pharyngeal ramus passes between the two epibranchials and gives off a medial branch which passes beneath the mucosa towards the third pharyngeal bone, and a lateral branch, V3E, which passes onto the anterior surface on the third epibranchial and then down it between the two rows of gill rakers. The remainder of V3E joins branch V2F at the top of the third ceratobranchial. The pretrematic ramus (V3PR) then continues ventrally down the third epibran- chial and ceratobranchial to the end of the latter underneath the medial row of gill filaments. The posttrematic ramus of the third vagal branchial ramus (V3PO), after departing from the pretrematic ramus, passes ventroanteriorly and gives off a gill raker branch V3B which courses over the proximal end of the fourth cer- atobranchial and onto its anterior surface be- tween the two rows of gill rakers for the anterior third of this bone. The rest of the posttrematic passes the joint between the fourth epi- and cer- atobranchials, medial to the levator posterior (LEP) muscle. It then crosses the dorsolateral surface of the obliquus posterior muscle (OP) and at the top of the fourth arch detaches branch 3BC which innervates the adductor IV (AA4) branchial muscle. The postrematic then courses down the fourth ceratobranchial underneath the lateral row of gill filaments, near the end of this bone detaching branch 3BD which passes me- dially and innervates the transversus ventralis IV (TV4) muscle. The end of the posttrematic branch innervates the floor of the pharyngeal cavity at the base of the fourth gill arch. En route down the fourth ceratobranchial, the post- trematic detaches about six short gill raker branches, each of which innervates a series of gill rakers and adjacent mucous epithelium on the anterior surface. FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGK1I 37 Fourth vagal branchial trunk After departure of the first three vagal bran- chial rami, the vagus consists of the intestinal and cardiac rami and the fourth vagal branchial trunk. Only the first three esophageal rami which detach segmentally are illustrated. The intestinal and cardiac rami were not further studied. The ganglion for the fourth vagal bran- chial trunk forms on the dorsolateral surface of the third ganglion. Near the anterior end of the esophagus, the fourth vagal trunk separates into pretrematic and posttrematic rami, V4PR and V4PO. respectively. The pretrematic (V4PR) ra- mus passes anteroventrally towards the pharynx where, at the junction of the fourth ceratobran- chial and fourth epibranchial, it detaches a small branch (not labeled on Fig. 19) which passes medially under the fourth epibranchial bone, in- nervating the dorsal extension of the medial row of gill filaments. The rest of the fourth pretrem- atic ramus continues ventrally about halfway down the fourth ceratobranchial beneath the medial row of gill rakers. Although the gill slit behind the fourth arch is reduced to about half size, the medial row of filaments extends some distance further, but the innervation to it was not detected. The fourth vagal posttrematic ramus (V4PO) drops ventrally towards the dorsal end of the fifth ceratobranchial bone, passing along the posterior surface of the obliquus posterior mus- cle (OP), detaching a branch to this muscle (the upper branch of V4B), and another (the lower branch of V4B) to the adductor V (AA5) muscle. Just past the dorsal head of the fifth ceratobran- chial, the fourth posttrematic vagal ramus de- taches branch V4E, which in turn divides, one part innervating the pharyngoclavicularis inter- nus (PCI) and the other the pharyngoclavicularis externus muscles (PCE). Branch V4D detaches at the same point as V4E and divides: one branch innervates the transversus ventralis IV muscle (TV4) and another branch (not shown) innervates the floor of the pharynx directly pos- terior to the fifth ceratobranchial. The remainder (V4C) of the fourth posttrematic ramus inner- vates the teeth and mucous epithelium of the fifth ceratobranchial. Summary of Gill-Arch Muscle Innervation Glossopharyngeal nerve innervates: (1) Levator internus II (LIZ) by branch Gl (2) Levator externus I (LEI) by branch G3 (3) Rectus ventralis I (RV1) by branch G8 First vagal branchial ramus innervates: (1) Levator internus III (LI3) by branch VIA (2) Obliquus ventralis II (OV2) by branch VIC Second vagal branchial trunk innervates: (1) Levator posterior (LEP) by branch V2A (2) Levator externus IV (LE4) by branch V2B (3) Obliquus dorsalis III (OBD3) by branch V2C (4) Transversus dorsalis II (TD2) by branch V2D (5) Obliquus ventralis III (OV3) by branch V2J (6) Rectus communis (RCOM) by branch V2G (7) Rectus ventralis V (nerve supply not shown on Figure 19) (8) Rectus ventralis IV (RV4) by branch V2H Third vagal branchial trunk innervates: ( 1 ) Retractor dorsalis (RETD) by branch V3A (2) Adductor IV (AA4) by branch 3BC (3) Transversus ventralis IV (TV4) by branch 3BD Fourth vagal branchial trunk innervates: (1) Obliquus posterior (OP) by upper branch of V4B (2) Adductor V (AA5) by lower branch of V4B (3) Pharyngoclavicularis internus (PCI) by branch V4E (4) Pharyngoclavicularis externus (PCE) by branch V4E (5) Transversus ventralis V (TV5) by branch V4D Ramus opercularis vagi innervates: (1) Protractalis pectoralis (PRP) by branch PRPE Lateral Line Nerves of the Trunk Herrick (1899) did not consider the nervus lin- ae lateralis to be part of the vagal nerve. He treated it as a separate entity morphologically, since it has a different origin in the medulla ob- longata and is physically separate from the va- gus nerve, although it has a connection with the vagus by general cutaneous fiber bundles. Some of the latter join the ramus supratemporalis vagi from the vagus. The origin of the lateral line 38 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 nerve is from the acoustico-lateralis center in the medulla near that of the auditory nerve (Her- rick 1899). The terminology for the trunk lateral line nerves follows Freihofer (1972). The lateral line of the trunk of most fishes is usually a linear series of scales along the side of the body, each scale having a bony tube or canal opening laterally by a pore onto the surface. A relatively large lateral line canal organ lies about midway inside the tube of each scale. In Poly- centrus there is only one tubed lateral line scale. It is the first scale after the posttemporal canal. Although there is virtually no scaled or mem- branous lateral line canal on the trunk in Poly- centrus, the lateral line nerve on the trunk is well developed. The branches of the lateral line nerve innervate short vertical rows of small, free lateralis organs located on certain scales, the lat- eralis scales forming longitudinal rows as de- picted in Figure 21. Nervus Linae Lateralis The nervus linae lateralis (NLL) arises from the brain about halfway down the side of the medulla oblongata and a little anterior to the root of the nervus glossopharyngeus (Figs. 28 and 30). NLL courses posteriorly, almost horizon- tally, close to the medulla. As NLL continues posteriorly, it comes to lie lateral to the emerging root of the nervus vagus at the midside of the medulla. The two roots proceed separately lateroposteriorly to their common foramen in the exoccipital bone at the top of the bulge of the wall of the otic bulla, the nervus linae lateralis lying dorsal and lateral to the nervus vagus (Fig. 4). A few ganglion cells form on the dorsal surface of NLL before it passes out through its foramen. More ganglion cells form outside the cranium in the recess be- tween the otic wall of the bulla and the lateral horizontal wall of the exoccipital. Then ganglion cells form a large swelling which continues for some distance as NLL passes posterolaterally through the head kidney. Shortly before leaving the head kidney, the sizeable ramus supratem- poralis vagi is detached (Fig. 5), passing dorsally and a little posteriorly towards the medial side of the supratemporal canal. This ramus is de- scribed in a preceding section. Immediately anterior and medial to the supra- cleithrum, the nervus linae lateralis splits into two large rami, NLL1 and NLL2 (Fig. 21). Ra- mus NLL2, the dorsal longitudinal "collector" lateral line nerve, passes dorsoposteriorly me- dial to the shoulder girdle and detaches two branches en route. The larger of these, NLL2a, then gives off a relatively short branch which can be designated the dorsal fin branch. It in- nervates the vertical row of free lateralis organs on a scale pocket dorsal to the posterior opening of the posttemporal canal (Figs. 17 and 21). The rest of NLL2a curves anterodorsally and then posteriorly, coursing to the anterior end of the dorsal fin where it innervates free lateralis or- gans on two scale pockets anterior to this fin (Fig. 21). The other branch, NLL2b, innervates the scale pocket directly posterior to the post- temporal canal, which is the only lateral line scale on Polycentrus . The main part of NLL2, the dorsal longitu- dinal collector lateral line nerve, arches dorso- posteriorly beneath the skin to nearly halfway to the dorsal fin, where it levels off and contin- ues posteriorly gradually dropping ventrally to- wards NLL1 which it finally overlies at the pos- terior end of the soft anal fin. En route, NLL2 detaches ten long ramuli which innervate free lateralis organs on ten individual scale pockets along the base of the spinous dorsal fin, and two long ramuli which similarly innervate free lat- eralis organs on two scale pockets near the base of the soft dorsal fin (Fig. 21). En route it also gives off thirteen shorter ramuli, including NLL2b, twelve of which innervate free lateralis organs on twelve scale pockets that lie horizon- tally along a line one-third to one-fourth of the way towards the dorsal fin. Ten of these branch- es occur on the anterior half of the body. The thirteenth ramulus innervates free lateralis or- gans on a scale pocket a little below NLL2, not far from the caudal peduncle. The main trunk of NLL2 terminates by splitting into two ramuli which supply free lateralis organs on two suc- cessive scale pockets anterior to the caudal fin. The branches NLL1 and NLL2 do not rejoin posteriorly. The other ramus, NLL1, the horizontal sep- tum lateral line nerve of the nervus linae later- alis, continues straight to the caudal fin. En route it detaches three commissural or collector branches, NLLla, NLLlb, and NLLlc, which join and form the dorsal longitudinal collector lateral line nerve, NLL2. Branch NLLlb de- taches a long ramulus which passes dorsally to innervate free lateralis organs on a scale pocket FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKI1 39 lying directly ventral to the sixth spine of the dorsal fin. The commissural branch NLLlc de- taches a ramulus that passes ventrally towards the anterior anal spines where it splits into three branches, each innervating free lateralis organs on a scale pocket directly dorsal to the anal spines. The main trunk, NLL1, next gives off two more ramuli, each innervating a scale pock- et and its free organs near the bases of anal spines. The penultimate ventral ramulus divides near the anal fin and innervates the free lateralis organs on three more scale pockets along the base of the fin. Lastly, a ramulus is detached which in turn divides into three more branches which supply free lateralis organs on three scale pockets along the base of the soft anal fin. The remainder of NLL1 courses posteriorly and bifurcates near the base of the caudal fin. The dorsal fork runs along the bases of the rays of the dorsal half of the fin and detaches a large ramulus which continues in the membrane be- tween the fifth and sixth caudal rays, innervating a long row of about 24 free lateralis organs. The rest of the dorsal fork passes to the skin of the dorsal surface of the caudal peduncle where it innervates, in succession, free lateralis organs on four small scale pockets, one of these branch- es innervating a scale pocket at the base of the fourth caudal ray. The ventral fork continues in the membrane between the eleventh and twelfth caudal rays, innervating a long line of about 24 free lateralis organs. Discussion Free Cephalic Lateralis Organs Free cephalic lateralis organs (pitorgans) or their derivatives are found in all the classes of jawed fishes. The pitorgans are often rather closely associated with the cephalic lateralis ca- nals. The organs may occur in clusters or lines or in both arrangements on the same fish. In Polycentrus they are in clusters at the anterior end of the head and increasingly arranged in lines more posteriorly. Although considerable information exists on pitlines (see Disler 1971; Stensio 1947), there is not much information on these organs for per- ciform fishes. Stensio (1947) broadly homolo- gizes six pitlines of the cheek and lower jaw in all classes of gnathostome fishes and of amphib- ians. The purpose here is merely to compare the pitlines of Polycentrus with those of some other percoids. with Menidia, and with a few lower groups to obtain an idea of the degree of pitline specialization in Polycentrus. Simple locational names for various pitlines are used for conve- nience. Comparison with Perca fluviatilus Perca (Disler 1971: fig. 56) has four organs medial to the anterior end of the nasal canal and a longitudinal row of seven or eight organs ven- tral to the anterior and posterior narial openings. There are three organs in the location of the an- terior pitline of Amia (Allis 1889: pi. 42, fig. 49) and six organs in the location of the supratem- poral row (the posterior pitline of Amia). Lastly, Perca has a vertical row of about six organs and an opercular row of about eight organs. These pitlines in Perca correspond to pitlines in Poly- centrus having similar location and innervation. Polycentrus has more organs at these locations. The main differences between Perca and Poly- centrus are that Polycentrus has, in addition to the above lines, well-developed supraorbital, in- fraorbital, and mandibular pitlines. Perca lacks these lines and presumably every organ of each line. Perca is a more generalized percoid in its swimming and feeding habits than is Polycen- trus. These extra cephalic pitlines in Polycen- trus, together with the development of pitlines on the trunk of the body and the lack of lateral line scales, suggest that the additional pitlines in Polycentrus are specializations. There are indications that the ancestors of percoids may have had a fuller development of the pitline system than do recent species. Nu- merous beryciforms such as melamphaeids, trachichthyoids, and stephanoberycoids have many free cephalic lateralis organs. Percopsi- forms have the system very well developed. So do myctophoids and various other protacan- thopterygians, not to mention ostariophysans. Pitlines are well developed in the percoid family Apogonidae, where its elaboration is apparently a specialization rather than a retained ancestral condition. Inspection of nandid genera for pit- lines shows that Nandus has the system least developed, and the others (Afronandus, Mono- cirrhus, and Polycentropsis) have it well devel- oped. The lines in nandids have lengthened, but whether a line can be completely lost (not a sin- gle free organ present where the line should be) and be redeveloped is uncertain. Both Polycen- trus and Apogon may be examples in which at least some lines redeveloped after having been 40 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 lost. One would think that as long as the facial and vagal lateralis roots are present, any partic- ular pitline could be completely lost and later reformed. Detailed comparative studies of pit- organs are needed and should prove most inter- esting. Comparison with Menidia Herrick describes for Menidia some twigs of a branch (SO. 14; Herrick I899:pl. 2, fig. 3) of the r. ophthalmicus superficialis facialis that supply free lateralis organs (g, h, and i) lying between the dorsal margin of the anterior narial opening and the anterior end of the nasal canal. These organs correspond to a cluster of organs in the same location in Polycentrus, but the in- nervation is different in Polycentrus , being from the r. buccalis facialis of the infraorbital trunk. If Herrick is correct, Menidia stands alone among teleosts, as far as I can determine, in its innervation of these snout organs. Examination of Sihler preparations of representatives of 85 families did not show any species with free lat- eralis organs in this area innervated from the supraorbital trunk. Herrick found other pit or- gans on the snout of Menidia to be innervated from the infraorbital trunk. These include three organs (a, b, and c; Herrick 1899:pl. 2, fig. 3) lying between the anterior and posterior nostrils and three more organs on top of the anterior end of the snout medial to the anterior nostril, one organ lying quite far medially. These pitorgans correspond in position and innervation to similar clusters of pitorgans in Polycentrus. In Menidia there are pitorgans lying below the orbit in the area of the missing part of the in- fraorbital canal that are innervated by the r. buc- calis facialis. They presumably represent the modified canal neuromasts from the missing ca- nal segment. In Polycentrus there is an infraor- bital row containing many more pitorgans than in Menidia which are innervated by the r. buc- calis, but in Polycentrus the canal and canal bones are still present, although there is only one canal neuromast in the fused second, third, and fourth infraorbital bones. The interesting question is, Do these pitorgans along the edge of these infraorbitals represent modified canal neuromasts or do they represent a proliferation of pitorgans that were never canal neuromasts but which formed or proliferated as the canal neuromasts disappeared? The implication by other authors seems to be that they presumably are modified canal neuromasts. Menidia also has one pitorgan at the dorsoan- terior corner of the opercle and four at the ven- troanterior corner, much as in Polycentrus (Fig. 2. branches TH4AA for the opercle, and TH9B02 for the subopercle; and Fig. 15), innervated by branches of the r. opercularis facialis. Menidia apparently has a reduced cheek pitline (either the vertical or horizontal cheek line of Ainia; see Allis 1889: fig. 42) innervated by branch M.VII 1 (Herrick 1899: fig. 3) supplying only one pit- organ, which is all Herrick found. The same branch, M.VII 1 of the r. mandibularis externus facialis, also innervates four organs over the horizontal arm of the preopercular canal and an- other organ at the base of the third pore of the preopercular canal. These four organs plus one organ more anteriorly correspond to the man- dibular pitline of Amia (Allis 1889: fig. 42) and to a similar line of organs in Polycentrus (Fig. 17). Herrick shows no pitorgans associated with the supratemporal canal in Menidia, whereas Polycentrus has a lower line (STL: Fig. 17) and a higher line (two scales above the supratem- poral canal, each bearing a row of pitorgans) innervated by the r. supratemporalis vagi. Comparison with cyprinids Pitlines are well developed in Phoxinus (Man- igk 1934: fig. 1). A number of lines correspond in position and innervation to those in Polycen- trus. A seemingly important difference in Phox- inus that is not found in Polycentrus and not noted in other fishes is the presence of lateralis fibers in the r. mandibularis trigeminus. These fibers supply pitorgans located in Phoxinus at the anteroventral corner of the cheek above the mandibular canal. In other fishes, organs in this location would be innervated by the r. buccalis accessorius. These pitorgans in Phoxinus could not be homologous with part of the postmaxil- lary or supramaxillary lines of Stensio (1947). Another unusual innervation occurs in Phoxinus for pitorgans lying just in front of the vertical arm of the preopercle and along its horizontal arm (Manigk 1934: fig. 1). These pitorgans in Phoxinus are supplied by branches of the r. hy- oideus. The same pitorgans and innervation oc- curs in Parasilurus (Atoda 1936). In Polycentrus the preopercular pitline is supplied by branches of the r. mandibularis externus facialis. It would seem most probable that the pitorgans in this location in Phoxinus are an independent devel- opment. They would not appear to be homolo- FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII 4! gous with any of the six pitlines of Stensio. An- other difference in Phoxinus is that pitorgans on the uppermost cheek region ventral to the pter- otic canal are supplied by the ramus oticus. Polycentrus lacks these pitorgans. Comparison with esocoids Esocids and umbrids have numerous ce- phalic pitlines (Nelson 1972), some of which lie in gaps in the cephalic canal system. Three of the pitlines of Polycentrus are compared with pitlines in corresponding places in esocoids. The lines are the subnasal, infraorbital, and supraor- bital. In Polycentrus the infraorbital and sub- nasal pitlines (Fig. 17) are innervated by branch- es of the r. buccalis facialis of the infraorbital trunk (Fig. 1, branches 3b, 3c, I02fg, and a ver- tical branch of I01d2 that goes to pitorgans be- low the posterior nostril) and by one branch (TH10A; Fig. 2) from the r. buccalis accesso- rius, which supplies pitorgans at the posterior end of the infraorbital pitline. Nerve fibers of the r. buccalis facialis come from the dorsal lat- eralis root of the facial nerve (Fig. 31) and course in the infraorbital trunk. The innervation for these three pitlines in umbrids and esocids is quite different from that in Polycentrus. Sihler nerve preparations of Esox vermiculatus and Umbra pygmaea show that these pitlines are all innervated by a branch of the r. buccalis acces- sorius facialis which detaches from the truncus hyomandibularis high up on the side of the cheek. The lateralis fibers constituting the r. bucc. ace. fac. belong to the ventral lateralis root of the facialis. Another pitline, the supraor- bital, is innervated in Polycentrus by the r. ophthalmicus superficialis facialis, the fibers of which belong to the dorsal lateralis root of the facial nerve, whereas in esocids and umbrids these pitorgans are innervated by fibers derived from the ventral lateralis root of the facial nerve. They course in the supraorbital branch of the r. bucc. ace. fac. These three cephalic pitlines of esocoids, therefore, are not homologous with pitlines in corresponding positions in Polycen- trus or with corresponding pitlines in numerous acanthopterygians. Nelson (1972: 16) states that for esocoids in which a segment of a cephalic canal has been eliminated, the canal neuromasts may be modi- fied into superficial pitorgans. As far as I have been able to determine, branches of the r. bucc. ace. fac, which innervate these pitorgans in esocoids, never innervate canal neuromasts. These branches appear to belong to a special pitline system represented in part at least by the ramus canalis lateralis facialis system seen well developed in Lampanyctus (Freihofer 1970; Ray 1950) and to which the r. bucc. ace. fac. belongs. It would seem worthwhile to entertain the thought that all pitorgans are innervated by a system of lateralis nerve fibers distinct from that which innervates canal neuromasts. The main difference between the two classes of lateralis fibers, if there are two classes, may be that lat- eralis fibers innervating canal neuromasts can induce bone formation, whereas lateralis fibers innervating pitorgans cannot. It would make sense to keep the "power" of bone induction in one system of fibers. The esocoids appear to be an exception to the general statement made by Nelson (1972) that pitlines are not useful in higher category classi- fication. The innervation of pitlines in esocoids may be particularly useful for this purpose. Comparison with Amia Polycentrus has several pitlines that have the same location and innervation as in Amia. These are the vertical pitline of the cheek (Allis 1889: pi. 42, fig. 49), the supratemporal (extrascapu- lar). the mandibular, and probably the anterior pitline. Polycentrus lacks the middle pitline (in- nervated by the glossopharyngeus nerve in Amia), the gular pitline, and the horizontal pit- line of Amia. Pitlines present in Polycentrus that are absent in Amia are the supraorbital, infraor- bital, chin, narial, opercular, subopercular, and preopercular pitlines. The interesting question is still unanswered of whether or not the narial pitlines of Polycentrus and other fishes corre- spond to modified canal neuromasts that result- ed from the loss of ethmoidal and antorbital ca- nals presumably present in the ancestors of teleosts. Cephalic Lateralis Canals and Neuromasts The cephalic lateralis canals and their organs for Polycentrus are shown in Figures 1, 2, 3, 5, 10, and 17. The number of neuromasts for each cephalic canal-bearing bone is given in Table 1 for Polycentrus , several other perciforms. Men- id ia. Gadus, and Amia. The head canals of Polycentrus are all en- closed in bone. There are four separate infraor- bitals including the lachrymal and the dermo- sphenotic (shown missing in all nandids by Liem 1970: fig. 3). Judging from Perca. Kuhlia (Table 4: OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 Table 1. The Number of Canal Neuromasts in Each Cephalic Canal-Bearing Bone.3-7 Name of Poly- Para- Archo- Canal cent rus* A mia Roccus labrax Kuhlia Perca plites Scomber Gad us Menidia 5 Nasal 1 3 1 1 1 ! 1 3 2 1 Frontal 4 3 4 4 4 4 4 4 3 5 Ethmoidal - 2 - - _ _ _ _ _ _ Antorbital - 4 - _ _ _ _ _ _ _ Lachrymal 4 2 4 4 4 4 3 4 5 2 2nd Infra2 1 1 1 1 I6 1 1 1 I 3 3rd Infra2 - 1 1 1 2 1 1 1 1 _ 4th Infra2 - 1 1 1 _ 1 2 1 1 _ 5th Infra2 1 1 1 1 1 1 1 2 1 _ 6th Infra2 r 1 l1 r 1 1 1' 1' 1 _ 7th Infra2 - r - - r 1' _ _ r I1 Pterotic 2 3 2 2 2 2 2 3 i 1 Supratemporal 2 4 3 3 3 4 3 3 3 3 Posttemporal 1 1 1 1 1 1 1 or 2 1 1 1 Preopercle 7 6 6 6 6 6 6 3 5 5 Articular 1 3 1 1 1 1 1 1 1 1 Dentary 4 7 4 3 4 6 4 4 6 6 1 This last infraorbital is the dermosphenotic. 2 Infra = infraorbital 3 It is assumed that the primitive number of infraorbitals in percoids is seven, counting the lachrymal as the first. 4 In Polycentrus the second, third, and fourth infraorbitals may have fused and also the fifth and sixth. s The primitive number of infraorbitals for atherinids is uncertain. The second infraorbital consists of two bones (Pranasus and Melanotaenia). There is plenty of space between the second infraorbital and the dermosphenotic for two or three missing bones. Herrick (1899) shows for M. beryllina eight large free lateralis organs in place of the missing infraorbitals. h The third and fourth infraorbitals have apparently fused as indicated by the presence of two canal neuromasts in the third infraorbital. 7 The species examined are A. calva . P. clathratus. K. rupestris , Perca flavescens, Archoplites intern/plus. S. japonicus, and M. beryllina. Two specimens were examined of Polycentrus and Kuhlia but only one for each of the other species. 1), and Lobotes, the generalized number of in- fraorbitals for percoids appears to be seven (counting the lachrymal as the first), but judging from Roccus and Paralabrax, it appears to be six. In Table 1 it is assumed that seven is the primitive number of infraorbitals for percoids. Polycentrus is specialized compared with Roc- cus, Perca, Kuhlia, Archoplites , and Paralabrax in apparently having infraorbitals 2, 3, and 4 as well as 5 and 6 fused, and in having only one canal organ in each compound bone. In Nandus (Liem 1970: fig. 20) the second infraorbital is missing, but the dermosphenotic is present. Af- ronandus (Liem 1970: fig. 18) has only the lach- rymal, the other infraorbitals having disap- peared. It would be particularly interesting to study the infraorbitals of Nandus and the other nandid species for the varying conditions of the canal bones, their neuromasts, and the pitorgans associated with the infraorbitals. Some under- standing might be gotten of the presumed evo- lution of pitorgans from modified canal organs, freed when their canals disappeared. Character- istics of the infraorbitals should be useful in nan- did taxonomy. Polycentrus is also specialized in having one less organ in the supratemporal, one more in the preopercle, and one less in the pterotic than do the above percoids. Archoplites appears more specialized than Roccus and Polycentrus in hav- ing one less organ in the lachrymal and one more organ in the fourth infraorbital. Polycentrus, therefore, is a little more specialized in the ce- phalic canals and their neuromasts compared to some generalized serranids and centrarchids. Polycentrus differs from the five other per- coids in the innervation of the two pterotic canal neuromasts. Both of its neuromasts are inner- vated by the ramus oticus, whereas in Roccus, Kuhlia, Paralabrax, Archoplites , and Perca the second organ is innervated by the r. supratem- poralis vagi. Polycentrus appears to be special- ized over the other percoids in the pterotic canal organs. Compared with the head canals of Scomber (see Allis 1903) and Gadus (see Cole 1898), those FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII 43 in Polycentrus are more generalized in several respects. Instead of the single nasal canal organ present in Polycentrus and many other percoids and perciforms (in fact in most spiny-rayed fish- es). Scomber has three and Gadus two organs in this canal. Study of the innervation of the nasal canal organs in Scomber and Gadus is nec- essary for understanding the significance of these differences in number of nasal organs. In Scomber the anteriormost organ is inner- vated from the infraorbital trunk (by the r. buc- calis facialis), which fact suggests fusion of a prenasal ossicle onto the nasal, a feat which is very rare in teleosts, if not unique. Out of more than 90 families of teleosts examined, the Scom- bridae is the only one found so far with this ev- ident condition. The other two nasal canal or- gans are innervated from the supraorbital trunk and are evidently derived from an original single organ. The two rear nasal canal organs in Ras- trelliger kanagurta are very close together and are innervated by a branch that divides just be- fore reaching the two organs, which suggests the original single organ has divided. The nasal canal bone of Gadus has an even more interesting history than has the nasal bone of Scomber. Study of the innervation of the frontal and nasal canal organs in Sihler prepa- rations of Microgadus and Merluccius (Gadi- dae), Physiculus (Moridae), and Malacocephal- us (Macrouridae) indicates that the anteriormost frontal canal organ has migrated forwards over the floor of the frontal canal and onto the rear of the floor of the nasal canal, the original nasal canal organ having moved onto the anterior half of the nasal canal. Examination of the nasal and frontal canals in many families of paracanthop- terygian and acanthopterygian fishes for the number of canal organs in these bones reveals that there is always one organ in the nasal and four in the frontal in all families examined except in the gadoids, ophidioids, and the beryciform Stephanoberyx. Cole's figure of Gadus (Cole 1898:pl. 22, fig. 2) shows two nasal and three frontal canal organs located in the posterior half of the frontal, the anterior half of the frontal being empty of organs. The ophidioids that were examined (Brotula, Lepophidium, Dicrolene, and Chilara) agree with the gadoids in the num- ber of organs in the nasal and frontal, their in- nervation, and the lack of organs in the anterior half of the frontal. Zoarcids have one nasal and three frontal canal organs. Though the ophid- ioids and gadoids share a very unusual and rather surprising specialization of the nasal bone, it is not unique to them. Stephanoberyx, as already mentioned, also has it. The nasal bone in the three groups is always spacious and curved rather steeply downward around the an- terior end of the olfactory organ. The original nasal canal neuromast is located in the anterior half of the canal about at the ventral bend in the canal. Both nasal canal neuromasts have mi- grated anteriorly, the original nasal neuromast into the front end of the canal and the posterior neuromast into the rear of the canal. Stimuli for the nasal canal organs apparently come from a ventral direction. Though this condition of the nasal canal is rare, it is the result of processes that could plausibly happen more than once in teleosts. It surely has occurred independently in Stephanoberyx. Whether it has or not in the ga- doids and ophidioids remains to be seen. Compared with other spiny-rayed fishes ex- amined, the nasal canal and its bone in Polycen- trus is in a generalized state, having only one canal neuromast and almost no membranous ex- tension anteriorly. The nasal canal of some per- coids has an anterior membranous extension of greater or lesser extent, and sometimes there is a canal neuromast in it. In the latter instance, the membranous walls are thickened (formed of secondary cartilage from the dermis) and may have the shape of a small infraorbital canal bone. Examples are found in some lutjanids and po- madasyids. There may be one prenasal bone with a canal neuromast, as in the Toxotidae, or there may be two separate prenasals, one mem- branous and one bony (Carangidae), or both bony and separate (Coryphaenidae), or both bony and fused but separate from the nasal (Rachycentridae and Echeneidae). These per- coids with two prenasals (no other percoids hav- ing two have been found) appear to share the same specialization and very likely form a natu- ral, related group. Nematistius also was found to have a small, partially ossified prenasal canal unit with a neuromast. The Sciaenidae and Polynem- idae have a complex prenasal membranous canal development containing neuromasts. All of the additional prenasal canal units, whether mem- branous or ossified, are innervated from the in- fraorbital trunk. The nasal canal of berycoids, compared with that of Polycentrus, other percoids, and, in fact, with that seen in all other Sihler-prepared spec- 44 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 imens and in all published accounts, is strikingly different and specialized. The character consists of two (or one) secondary canal neuromasts in addition to the single original (primary) neuro- mast. The secondary neuromasts lie very close to the anterior edge of the floor of the nasal ca- nal, one organ near each lateral corner of the canal, and are innervated from the infraorbital trunk. The original nasal canal neuromast lies near the midlength of the canal and is innervated from the supraorbital trunk. The berycoids all have this character (at least one species of each family examined), but the stephanoberycoids, including melamphaeids and gibberichthyids, do not. Polymixiids have what appears to be an earlier development of the ber- ycoid condition. In Polymixia there are three free lateralis organs in a membranous canal that passes across but just outside of the entrance to the nasal canal. This membranous canal is con- nected across the tip of the snout with a similar canal on the other side of the head. Another lateralis organ lies at the midpoint of the cross- ing canal. The stephanoberycoids have what ap- pears to be a still more generalized condition in that there is a row of free lateralis organs in the skin across the tip of the snout in place of the membranous canal of Polymixia and a somewhat enlarged free lateralis organ in the skin just out- side each lateral corner of the opening in the nasal canal in place of the canal organ inside the nasal canal near each corner in berycoids. The mode of formation of the secondary nasal canal organs of berycoids is what makes this nasal canal specialization especially different from that in other fishes. In berycoids free lat- eralis organs close to the nasal canal opening have apparently been simply engulfed by the bony nasal canal without first being formed in a prenasal ossicle. In carangids, rachycentrids, echeneids, coryphaenids, and other groups, the prenasal ossicle or ossicles do not fuse onto the nasal bone. In Scomber a prenasal ossicle un- doubtedly has fused onto the nasal bone. In ber- ycoids there are no indications of such fusion; the one or two added canal neuromasts lie very close to the anterior edge of the nasal bone, there is no pore marking a fusion, and there is no bend or irregularity indicating a junction of two bones. It appears that in the berycoids we have an example, surely very rare, of two free transverse organs (reduced to one organ in some berycoids) being, in effect, "captured" (engulfed) by a na- sal canal bone! The berycoid nasal canal bone specialization would seemingly remove the ber- ycoids from being considered the ancestral source of percoids. The same statement may hold for the stephanoberycoids which have what appears to be an earlier stage of the polymixiid condition. This character state in beryciforms will be presented in a separate paper. It may be added that beryciforms have other specializations of the cephalic lateralis system. In stephanoberycoids the supratemporal canal is actually in communication with the nasal ca- nal and the frontal canal via a large lateralis chamber lying in the interorbital area over the frontals. In melamphaeids the lachrymal canal is in communication with the nasal canal. These developments are rare or unique in teleosts. In summary, two generalizations might be made about the innervation of the snout region for teleosts from conditions observed in Poly- centrus and Sihler nerve preparations of repre- sentatives of 85 families. The lateralis innerva- tion of the supraorbital trunk ends with the nasal canal bone. Any pitorgan development on the snout will be innervated from the infraorbital trunk. Any new canal and canal neuromasts be- yond the anterior end of the nasal canal will also be innervated from the infraorbital trunk. A sim- ilar generalization applies to the general cuta- neous innervation of the supraorbital trunk. In most of the fishes observed, it ended about at the anterior end of the nasal bone or a little be- yond it. Only in the atherinomorphs and holo- centrids did it extend significantly further, going to the upper jaw as a large nerve. Innervation of the Upper Jaw In Polycentrus the upper jaw is supplied with general cutaneous innervation by the inferior ramulus of the ramus maxillaris trigeminus (103; Fig. 1) and with gustatory innervation by the anterior ramus of the palatine nerve (Fig. 1). No other nerves go to the upper jaw, not even from the supraorbital trunk, which itself is something of a surprise if the upper jaw is considered a part of the snout. Polycentrus is representative of most teleosts in innervation of the upper jaw. One exception is Menidia (Herrick 1899; fig. 3, the yellow branch to the upper jaw). In Menidia the supraorbital trunk is continued out to the tip of the upper jaw, supplying it rather heavily with general cutaneous innervation. The nerve is FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII 45 large, as seen on Sihler nerve preparations of various atherinomorphs. Of 85 families, only the seven atherinomorph families examined and the Holocentridae had the premaxillary extension of the supraorbital trunk. In the Holocentridae the functional component is, presumably, also gen- eral cutaneous. Cheek Muscle Innervation The pattern of innervation of the cheek mus- cle in Polycentrus (Fig. 6) reflects the partial subdivision of the adductor mandibulae into three parts called A,, A2, and A3 (Fig. 22), branches I02c and I02d innervating A,, branch I02e innervating A2, and the hatched parts of 102 innervating A3. The pattern in Polycentrus is generalized for percoids. In fact, most of the other percoids examined had more distinctive patterns of innervation of the cheek muscle than does Polycentrus, each being a little different from the others. The sciaenids were especially distinct, the A,/3 muscle in some species being developed as fully as the A,/3 in percopsiforms, including its pattern of innervation. Atherino- morphs (7 families examined) have an innerva- tion pattern distinct from that of all other fami- lies studied except gasterosteids in which it is the same. Much can be learned of systematic interest from the cheek muscles by study of the pattern of innervation within the muscle. Results of a study of the Ax(3 muscle are being prepared for a separate paper. Correct Name for Ramus Lateralis Accessorius Herrick (1899: fig. 3) describes three ramuji from the r. lateralis vagi which join the r. recur- rens facialis to form the r. lateralis accessorius facialis (RLA). These ramuli join RLA on the posterior part of the head above the pharyngeal area and on the anterior part of the trunk. Her- rick indirectly derives these ramuli from a small bundle of fibers (about 20) which detach from the root of n. glossopharyngeus, this small bun- dle joining intracranially the root of the ramus lateralis vagi (r. lat. vagi). The fibers are of small to medium diameter, considerably smaller than lateralis fibers to canal neuromasts, according to Herrick, but larger than average communis fi- bers. Herrick could not trace these medium- small fibers from the glossopharyngeus through the ganglion of the r. lat. vagi. He assumed that fibers of the same size observed leaving the oth- er side of the ganglion were the same as the ones observed entering it, that is, that they were from the 20 fibers from the glossopharyngeus. He rather confidently identifies the three ramuli from the r. lat. vagi which appear to join RLA as being derived from the small bundle of fibers from the root of the glossopharyngeus. He fur- thermore assigns them to the communis system. Herrick's reasons, others in addition to those just given, are not very convincing. The use of the name ramus lateralis accessorius, therefore, really rests upon the fact that this nerve is made up of gustatory fibers from both the facialis and vagus (or glossopharyngeus) nerves. In Polycentrus no such ramuli from the r. lat. vagi were observed to join the recurrent facial ramus. In Polycentrus there is an intracranial vagal ramus that passes up to the parietal bone, and on some specimens it passes out of the cra- nium through the same foramen as does RLA, but on other specimens it passes through its own foramen close to that for RLA. In the latter specimens it was observed to pass to overlying skin and to skin lying anterior to its cranial exit. As far as could be determined from serial sec- tions of Polycentrus, it was seen to be an intra- cranial part of the rami cutanei dorsales vagi. It would be carrying general cutaneous innervation to the top of the head. Menidia lacks this intra- cranial vagal ramus. Herrick equates the three extracranial ramuli from the r. lat. vagi of Men- idia with this vagal ramus that is present in many other fishes (see Freihofer 1963 for examples). It may be equivalent as Herrick thought, but what seems quite doubtful from Herrick's dis- cussion of these three ramuli is that they are of the communis component and that they join RLA and presumably course some distance with it. On a Sihler nerve preparation of the atherinid Atherinops affinis, no ramuli from the r. lat. vagi were observed to anastomose with RLA. Ath- erinops also lacks an intracranial vagal ramus to the parietal. These three ramuli of Menidia and the intracranial vagal ramus of Polycentrus and other fishes need more study. If they prove not to be communis, that is. if there is no vagal com- munis contribution to the formation of RLA. there would be reason for changing the name of RLA to simply that of the ramus recurrens fa- cialis, in recognition of its purely facial com- munis composition. The facial part of RLA is much larger than is the vagal in apparently all teleosts having RLA. One disadvantage of using 46 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 the name RLA is that it implies that the nerve is an accessory lateral line nerve of the acous- tico-lateralis system, which it is not. The term RLA should stand until the question of the con- tribution of the vagal communis is resolved. Trunk Lateral Line Nerves The pattern of the trunk lateral line nerves of Polycentrus (Fig. 21) is especially interesting because it shows some ventral and dorsal seg- mental lateral line branches which previously have been known only in various lower, non- acanthopterygian fishes and in a less-developed state in zoarcids, gobiids, and mugilids (Frei- hofer 1970, 1972). There is one basic difference between the Polyce ntrus pattern and that of oth- er fishes having ventral segmental lateral line nerves. In Polycentrus as well as in the other 20 or so percoid families that have been examined, there is a dorsal longitudinal collector lateral line nerve. Other perciformes examined have this collector also, but the zoarcids, gobiids, and mugilids do not have it. The atherinomorphs all lack it, as do other groups examined that are classified lower than the acanthopterygians and paracanthopterygians. Some of the paracan- thopterygian fishes develop a dorsal longitudinal collector lateral line nerve at least towards the distal end of the dorsal longitudinal ramus. The ventral segmental lateral line branches in Poly- centrus, of which there are five, are a secondary development on a basic percoid pattern and is apparently associated with the specialized swimming habits of Polycentrus . It would be in- teresting to see the lateral line nerves of nandids more generalized than Polycentrus, especially Nandus. It would take very carefully preserved specimens to provide the information, but the distribution of free lateralis organs on the head and trunk of all nandid genera should be deter- mined. The results should have systematic sig- nificance for nandid classification. Polycentrus is a secretive fish which stalks its prey by an extremely slow forward movement made by the beating of its transparent soft dorsal and anal fins, its mode of forward progress, its coloration, and its body shape resembling a drifting dead leaf. When startled or after attack- ing a prey fish, Polycentrus can move quite rap- idly backwards from its position near the surface to its retreat near the bottom in a hole or pot. The head and trunk lateral line system may re- flect specializations for such swimming behav- ior. The lateralis organs of the trunk are all free or naked organs borne on scales, a series of about eight organs on each such scale, the lat- eralis-bearing scales being arranged in rows fol- lowing the main contours of the trunk (Fig. 21). The lateral line on the head is also specialized in that there are large neuromasts in the head lateralis canals as well as free organs arranged as shown in Fig. 21. The distribution of free lateralis organs on the trunk of Polycentrus illustrates to what degree lateralis organs can migrate and their nerves fol- low them. The question arises for the zoarcids, gobioids, and mugilids as to whether these groups have lost all traces of the basic percoid pattern or whether they ever had them. The large number (20 to 25) of free lateralis organs on the inside of the chin between the anterior ends of the dentaries is interesting in that a similar aggregation was observed on var- ious other percoids. It is apparently an impor- tant location for receiving lateralis stimuli, which in Polycentrus may serve a prey-locating function. An External-Internal Lateral Line Canal Nerve Relationship Worthy of special note is a branching rela- tionship observed on a number of ramuli going to individual neuromasts of the head canals (see branches to second and third pores of lachrymal canal. Fig. 1 . and SORB 4. SORB 1 1 . and SORB 1 la. Fig. 3). A similar relationship was also ob- served for lateral line scales on the trunk of vari- ous fishes. In this relationship a neuromast ramu- lus detaches from a main nerve ramus and courses alone towards its canal neuromast, but before reaching its canal neuromast. the ramulus itself detaches a branch which curves away and passes some distance to skin or membrane around an adjacent canal pore. In some in- stances, on Sihler nerve preparations this branch to the membrane around the pore ended in branchlets that resembled in appearance those that elsewhere were known to be innervating free lateralis organs. Such organs occur in the skin along the supraorbital and infraorbital ca- nals (Fig. 17) and elsewhere. If the ramulus were carrying only general cutaneous innervation, it would seem as practical, a distribution to have such fibers course in other rami that carry the main cutaneous innervation. The arrangement of a canal neuromast ram- FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGK11 47 ulus closely associated with a ramulus innervat- ing free lateralis organs in the skin would allow for the reception of differences between lateralis stimuli inside and outside the canals for each such location. Its development mPolycentrus is no doubt associated with this fish's very slow swimming habits, but it was observed also in other fishes, even for the trunk lateral line scales. Herrick (1899) briefly described a few of these branches on the head of Menidia but did not comment on them. Radix Profundus The complex relationships of the radix pro- fundus with the oculomotor nerve and trigeminal sympathetic ganglion in Polycentrus (Fig. 14) are quite similar to those of the perciform Ura- noscopus (Young 1931: text-fig. 8). There is a difference in Menidia that may be significant systematically. Herrick (1899) found that a rec- ognizable intracranial profundus root and gan- glion are missing in this atherinid. Since the cil- iary nerves are present in Menidia , the root and ganglion of the profundus must be present also, but apparently they are fused with the trigeminal root and ganglion, a condition which may be representative for atherinomorphs. A Stretch-Receptor Nerve to Base of Maxillary Tendon Especially interesting is a branch (I02fl: Figs. 6 and 10) of the r. mandibularis trigeminus which ends in a dense ramification of nerve fibers in the tendinous mucosa on the inside of the mouth, the innervation being directly in front of the anterior edge of the quadrate near the artic- ulation head of this bone. This tendinous mem- brane fans out towards the ventral end of the maxillary tendon. Branch I02fl may innervate stretch-receptor organs in this membrane. A similar branch was observed on a number of oth- er kinds of fishes. It was a large branch in a goatfish. Parupeneus porphyreus. A similar branch occurs in Menidia, but Herrick (1899) did not suggest any stretch-receptor innervation for it. It should be of interest to functional anat- omists studying jaw mechanisms. Simplifying Cranial Nerve Studies The fifth, seventh, ninth, and tenth cranial nerves are the most complex in their branching and number of nerve components, and for these reasons they hold the most interest for system- atists. Of these four cranial nerves, the fifth and seventh rank above the ninth and tenth. Broader taxonomic coverage can be had by concentrat- ing only on the fifth and seventh nerves, or by restricting the study even further to a certain trunk, ramus, or even to only a single larger branch of a ramus. The nerve chosen should be an integral unit, complete in itself, and not parts of two nerves or character complexes. It is also best to chose only one nerve com- ponent in a nerve trunk or ramus rather than include all components with all their branches. For example, one of the character complexes selected for comparison with Polycentrus was the lateralis component in the supraorbital trunk. Only the nasal and frontal bones were included. These seemed to form a natural mor- phological unit for this component in this nerve trunk. For practical purposes comparative studies can be made directly from Sihler nerve prepa- rations without recourse to serial-section tech- niques and involved neurological research. Prior grounding in the important nerve references em- ploying functional component analysis is, of course, essential. A brief listing of the most im- portant of the longer studies is given in the "In- troduction.** There are huge gaps in the taxo- nomic coverage in the nerve literature. The gaps can be filled effectively by a reference collection of Sihler nerve preparations. The nerve components of the various trunks, rami, and smaller branches can be worked out with relative assurance in most instances by study of Sihler nerve preparations and dissec- tions of preserved specimens. The dissections should expose the roots and ganglia of the tri- geminus, facialis, glossopharyngeus, and vagus nerves. The motor and lateralis components are not difficult to determine because their end or- gans are relatively large. Since free lateralis or- gans may be lost in the handling and preparation of specimens, the distribution of these organs should be plotted from freshly and carefully pre- served specimens (Fig. 17). Such a drawing is useful in helping assign terminal branches in a particular area of a Sihler preparation to the lat- eralis component. The gustatory component is difficult to determine unless the fibers course more or less as independent nerves for most of their length. Taste (terminal) buds located on the external body surface are too small to be seen except microscopically. Most of the gustatory 48 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 system will be represented by the distinctive branches of the recurrent facial and palatine nerves. Dissection of the geniculate ganglion should disclose the presence of larger bundles of gustatory fibers leaving this ganglion and en- tering the supra- and infraorbital trunks, but since these fibers disappear into the branches of these trunks, appropriate microtechnique meth- ods are necessary for determining their distri- bution. For most systematic purposes gustatory fibers entering these two trunks can be ignored. For practical purposes the last component, the general cutaneous, is what remains after the oth- er three components have been determined. In fishes, general cutaneous fibers terminate in free nerve endings in the skin or in special tactile elaborations of skin, such as cirri and other skin flaps, or in barbels or barbel-like structures. After determination of the functional compo- nents at the periphery of the nerves, the pres- ence of a component can be shown diagram- matically in drawings by a distinctive symbol, the fiber bundles of each branch being brought together as they course centrally towards the cranial roots and ganglia and to the brain. An example in which these simplified approaches were taken in a systematic study is that by Springer and Freihofer (1976). Short cuts such as those suggested above are necessary if nerves are to be used in the clas- sification of fishes. Basic, descriptive neurolog- ical studies are still needed on numerous groups. It may fall to the lot of some systematists to do them. Neurologists have seemingly turned to other tasks. Summary 1. The courses of the trigeminus, facialis, glossopharyngeus, and vagus cranial nerves of a percoid fish, Polycentrus schomburgkii , are described in detail, and the functional compo- nents of the nerves determined as far as possible with the methods used. The closest groups with which Polycentrus could be compared in pub- lished accounts were Scomber (Scombridae) and Menidia (Atherinidae). Comparisons were also made from Sihler preparations of numerous groups (representatives of 85 families available) for selected nerves. 2. Nothing unusual was noted in the olfactory (I), optic (II), oculomotor (III), trochlear (IV), or abducens (VI), nerves. 3. The radix profundus in Polycentrus has the same relationships to the Gasserian ganglion. trigeminal sympathetic ganglion, ciliary gan- glion, and oculomotor nerves as it has in Ura- noscopus, as far as could be determined. 4. Polycentrus was compared with five per- coids (Roccus, Kuhlia, Perca, Paralabrax, and Archoplites) and several other groups of fishes for cephalic canal neuromasts and with addi- tional groups for cephalic free lateralis organs (pitorgans). 5. Polycentrus is more specialized than the above percoids, both in number of pitlines and in their size. 6. A pitline corresponding to the vertical pit- line of Amia is present and innervated from the truncus hyomandibularis by the ramus buccalis accessorius. The posterior end of the infraorbital pitline is also innervated by a branch of the r. buccalis accessorius, which represents a spe- cialization since the infraorbital pitline is usually innervated from the infraorbital trunk by the r. buccalis. This posterior part of the infraorbital pitline may represent the horizontal pitline of Amia that has moved up to the edge of the in- fraorbital. 7. Some pitlines of some fishes may not be homologous with corresponding pitlines of other fishes. Esocoids are an example. At least three pitlines in Polycentrus (the infraorbital, subna- sal, and supraorbital) are not homologous with pitlines in the same location in esocoids. These three pitlines in esocoids are all innervated by the r. buccalis accessorius from the tr. hyoman- dibularis, whereas in Polycentrus the first two are innervated from the infraorbital trunk by the r. buccalis and the last pitline (the supraorbital) is innervated from the supraorbital trunk. 8. Reflecting perhaps the greater develop- ment of the infraorbital pitline is a specialization of the infraorbital canal-bearing bones, a first step towards degeneration of the infraorbital ca- nals; the second, third, and fourth infraorbitals are fused and there is only one canal neuromast in the compound bone. In other respects the ce- phalic lateralis canal-bearing bones are a little more specialized (one less neuromast in the su- pratemporal and one more in the preopercular canals) than in Roccus, Paralabrax, Archo- plites , and Kuhlia . 9. Various clusters and lines of cephalic pit- organs should be useful in nandid taxonomy. 10. The innervation of the snout in fishes is an important area for comparison in systematic studies. The snout in teleosts is innervated from FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKI1 4') two sources: the supraorbital and infraorbital trunks. In Polycentrus the supraorbital trunk supplies one canal lateralis organ of the nasal canal, and the infraorbital trunk innervates ap- parently all of the free lateralis organs on the snout dorsomedial and ventral to the nasal bone. In some fishes there are important differences in this generalized condition seen in Polycen- trus. If there are further developments of the lateralis system on the snout, such as an exten- sion anteriorly of the nasal canal, they are in- nervated by the infraorbital trunk. Innervation of the nasal canal organ or organs should be de- termined in systematic studies because two (or three) lateralis organs in the nasal canal may in- dicate a fusion of the nasal canal bone (with one or two canal organs) and a prenasal canal (with one canal organ), the latter being innervated by the infraorbital trunk, or it may have other sig- nificance. An example of a group having a nasal and two prenasals (the anterior one membranous and the posterior one bony) is the Carangidae. Other percoids having two prenasals with fea- tures indicating a shared, derived specialization with the Carangidae are the Coryphaenidae (two bony prenasals, each separate and free from the nasal), Rachycentridae (two bony prenasals fused but free from nasal), and Echeneidae (same as Rachycentridae). Some other percoids having other specializations of an anterior extension of the nasal canal are the Sciaenidae and Polynem- idae (both with deep, complicated membranous extensions); Toxotidae (a broad, bony prenasal); and Lutjanidae (one membranous prenasal). The Scombridae is so far unique in having a bony prenasal fused to the nasal. 11. Compared with Polycentrus, other per- coids, and all teleosts examined, the berycoids have a quite different specialization of the nasal canal. It consists of one or two nasal canal sec- ondary neuromasts located close to the anterior edge of the floor of the canal and innervated from the infraorbital trunk. Polymixia exhibits a stage that could be antecedent to that of ber- ycoids. Stephanoberycoids have what may be the most generalized condition for beryciforms. It appears that in berycoids free lateralis organs lying close in front of the opening of the nasal canal were directly incorporated into the ante- rior end of the nasal canal without the prior for- mation of a prenasal ossicle that subsequently fused onto the nasal canal bone. The "capture" or engulfing mode of formation would be rare. if not unique. In any event, the nasal canal spe- cialization appears basic in berycoids. It indi- cates that neither stephanoberycoids, polymix- ioids, nor berycoids are the ancestral source of perciforms. There are other striking specializa- tions of the cephalic lateralis canal system of beryciforms. 12. The gadoids and ophidioids have a shared specialization of the nasal canal in which the anteriormost frontal canal neuromast has mi- grated into the nasal canal, giving that canal two neuromasts and the frontal canal only three, the usual number being four for almost all acan- thopterygians examined. Stephanoberyx also has this specialization but not Gibberichthys . The zoarcids have only three frontal canal neu- romasts, but only one nasal canal neuromast. 13. The general cutaneous component of the supraorbital trunk in Polycentrus ends on the snout posterior to the upper jaw, which is where it ends in most teleosts. In all atherinomorph fishes examined, it continues anteriorly as a large nerve onto the upper jaw. The only other group also found having a similar large extension onto the snout is the Holocentridae. The pre- maxillary extension of the supraorbital trunk carries general cutaneous fibers in atherino- morphs. The functional component is not yet known for holocentrids, but it probably is gen- eral cutaneous. 14. The pattern of branching of the ramuli from the ramus mandibularis trigeminus into the adductor mandibulae muscles of the cheek in Polycentrus consists of two ramuli leaving the ramus mandibularis trigeminus close together. Their ramifications in the subdivisions of the cheek muscle mass reflect the structure of the muscle. The pattern of nerve branching in the adductor mandibulae muscle can be important in understanding the subdivisions of this muscle, such as the origin of the A^ muscle. It also may have systematic significance. An example was discovered in comparing the pattern of Polycen- trus with that of the atherinid Menidia. The ath- erinomorphs as a group have a nerve pattern to the cheek muscle different from that of all other fishes examined except for the gasterosteids. 15. The recurrent facial ramus (RLA) is pres- ent in one of the basic percoid patterns (referred to as the Serranus pattern), characterized by an orbito-pectoral and a parieto-dorsal branch. 16. There are few or no lateralis fibers in the ramus hyoideus. 50 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 17. There are apparently few or no communis fibers in the ramus mandibularis trigeminus and r. maxillaris trigeminus. 18. The anterior ramus palatinus joins the r. maxillaris trigeminus on the upper jaw. Some groups of fishes lack this anastomosis (atherino- morphs being one). 19. There is a Jacobson*s anastomosis. 20. The ramus mandibularis internus facialis is present. 2 1 . A nerve possibly functioning mainly as an innervation for stretch receptors in the mem- brane and tendons associated with the base of the maxillary tendon was observed in Polycen- trus and some other percoids. 22. A double type of cephalic canal lateralis innervation was observed on Polycentrus and some other acanthopterygians. It consists of two branches detaching from a single lateralis branch that innervates a canal neuromast: one of the two canal branches innervates the canal neuro- mast, and the rest of the canal branch passes to the membrane around the adjacent canal pore, the membrane at least sometimes observed to bear free lateralis organs. 23. There is an intracranial vagal ramus which in Polycentrus is a branch of the ramus cutanei dorsales vagi. This intracranial vagal ramus does not course with the recurrent facial ramus. It does not contribute to the latter ramus. No vagal branch was seen to contribute to the recurrent facial nerve on the nape. The question of the intracranial ramus being of general cutaneous or communis component should be studied in other fishes. If the intracranial vagal ramus does not contribute communis fibers to the recurrent fa- cial nerve, then the name of ramus lateralis ac- cessorius should not be used and the name of recurrent facial nerve be used in its stead for the entire course of the nerve. 24. The trunk lateral line nerves show a basic acanthopterygian pattern of a so-called dorsal, longitudinal collector lateral line nerve. In ad- dition there are a number of dorsal and ventral segmental branches which innervate three rows of scales bearing free lateralis organs (pitor- gans): a row along the base of the dorsal fin; a row halfway between the dorsal fin and the hor- izontal septum; and a row along the base of the anal fin. There are two rows of free organs on the caudal fin: one on its upper lobe and one on its lower lobe. There is only one regular tubed lateral line scale, the first one. Each of these separate rows of free organs on a scale may rep- resent a canal neuromast that has migrated to- wards the base of a fin and subdivided into about eight smaller free organs; or each row of free organs on a scale may represent multiplication of a single pitorgan originally associated with each tubed lateral line scale. Such pitorgans were observed, one per lateral line scale, on some lateral line scales of other fishes. It was not observed on the single tubed scale of Poly- centrus. It is not known which of the possible origins is correct for the development of such free lateralis organs, either on the head or on the trunk of the body. 25. Some interesting systematic problems on the higher category classification of certain groups of fishes were disclosed in the compar- ative studies made between Polycentrus and groups represented in the nerve literature and from Sihler nerve preparations. 26. For systematic purposes the most useful cranial nerves to study are the fifth, seventh, ninth, and tenth, with the fifth and seventh being the most useful, if a choice has to be made. These cranial nerves are the most complex and offer the most characters. 27. From a consideration of the usefulness that nerves apparently have for studies on the classification of fishes and the great gaps there are in the taxonomic coverage of the nerve lit- erature for fishes, it is apparent that at least one basic descriptive study of the cranial nerves of a representative of each order is definitely need- ed. This research should be carried out by sys- tematists. Morphologists are no longer interest- ed in descriptive nerve studies. 28. Making the preceding recommendations much more feasible is the Sihler technique for staining nerves in a cleared, intact specimen. Acknowledgments My thanks go out to many individuals who helped make this study possible. Dr. George S. Myers gave the original breeding stock of Poly- centrus and encouraged continuance of the proj- ect. Dr. Stanley H. Weitzman helped locate "'populations" of Polycentrus in San Francisco aquarium stores, gave advice on techniques and on other matters. Dr. Richard Winterbottom kindly advised on the muscle terminology. Drs. Stanley H. Weitzman, William N. Eschmeyer, and Mr. Leonard J. V. Compagno critically read the manuscript. I assume full responsibility for FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKI1 51 any errors or omissions still in the paper and for the views expressed. The following individuals all kindly sent formalin specimens for use in the nerve processing: Dr. Gerald Allen, Mr. Eric Anderson, Drs. Gilbert Bane, Clyde Barbour, Gregor Cailliet, Bruce Collette, Mr. C. E. Daw- son, Drs. Hugh De Witt, Douglas Hoese, Rich- ard Ibara, Tomio Iwamoto, Mr. Shelley John- son, Mr. Susumu Kato, Dr. Leslie K. Knapp, Dr. Robert J. Lavenberg, Mr. Robert Lea, Drs. John E. McCosker, Robert W. McDowall, John W. Meldrim, Mr. George C. Miller, Drs. John R. Paxton, Theodore Pietsch, John E. Randall, Edward Raney, Richard Rosenblatt, Mr. Walter Schneebeli, Drs. Victor G. Springer, Jon C. Staiger, the late Mr. Franz Steiner, and Dr. Camm Swift. The late Mary Hayes Wagner helped greatly with all the final inking and la- belling of the drawings. Maurice Giles of the California Academy of Sciences contributed his photographic skills. Leonard J. V. Compagno again has been a patient listener and discussant. Much of the research was done at the California Academy of Sciences. It was begun at Stanford University. The help and support I received are gratefully appreciated. The research was sup- ported in part by NSF Grant GB-30551. 52 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 Literature Cited Ai i is. Edward Phelps, Jr. 1889. The anatomy and devel- opment of the lateral line system in Amia calva. J. 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Sci., ser. 4, 38(12): 215-264, 20 figs. . 1972. Trunk lateral line nerves, hyoid arch gill rakers. and olfactory bulb location in atheriniform, mugilid, and percoid fishes. Occas. Pap. Calif. Acad. Sci. 95: 31 pp., 12 figs. , Leonard J. V. Compagno, and William Rogers. 1977. Additional notes on the use of the Sihler technique of staining nerves of small, whole specimens of fishes and other vertebrates. Copeia 1977(3): 587-588. Gilmore, R. G., Jr. 1972. The cephalic nerve pattern and lateral line system of Hyporhamphus unifasciatus and Strongylura marina (Pisces: Exocoetidae, Belonidae). Mas- ter's Thesis. University of West Florida. 35 pp., 7 text-figs. Greenwood, P. Humphry, Donn E. Rosen, Stanley H. Weitzman, and George S. Myers. 1966. Phyletic stud- ies of teleostean fishes, with a provisional classification of living forms. Bull. Am. Mus. Nat. Hist. 131(4): 339-456, text-figs. 1-9, pis. 21-23, charts 1-32. Gupta, O. P. 1972. On the origin and innervation of the cranial and spinal nerves along with the autonomic nervous system of the Indian Gar-fish, Xenentodon cancila (Ham.). Anat. Anz. 131: 39-50, 4 figs. Hennig, Willi. 1966. Phylogenetic systematics. (Transl. by D. Dwight Davis and Rainer Zangerl.) University of Illinois Press. 263 pp., 69 figs. Herrick, C. Judson. 1897. The cranial nerve components of teleosts. Anat. Anz. 13(16): 425-431. . 1898. Experiments with the Weigert method. J. Comp. Neurol. 8: XXVII to XLIV. . 1899. The cranial and first spinal nerves of Menidia; a contribution upon the nerve components of the bony fish- es. J. Comp. Neurol. 9: 153^155, pis. 14-20. . 1900. A contribution upon the cranial nerves of the codfish. J. Comp. Neurol. 10: 265-316, pis. 21-22. . 1901. The cranial nerves and cutaneous sense organs of the North American siluroid fishes. J. Comp. Neurol. 1 1: 177-249, pis. 14-17. . 1903. The doctrine of nerve components and some of its applications. J. Comp. Neurol. 13: 301-312. Hollister, Gloria. 1934. Clearing and dyeing fish for bone study. Zoologica (N.Y.): 12(10): 89-101. Laurent, P., and S. Dunel. 1966. Recherches sur l'innervation de la pseudobranchie des teleosteens [in French. English summary]. Arch. Anat. Microsc. Morphol. Exp. 55: 633-656, 9 figs. Leach, E. H. 1946. Curtis' substitute for van Gieson's stain. Stain Technol. 21: 107-110. Liem, Karel. 1970. Comparative functional anatomy of the Nandidae (Pisces: Teleostei). Fieldiana: Zool. 56: 1-166, 66 figs. Maheshwari, S. C. 1965. The cranial nerves of Mastacem- belus armatus (Lacepede). Jpn. J. Ichthyol. 12(3/6): 89-98, 4 figs. Manigk, Wolfgang. 1934. Der Trigemino-Facialiskomplex und die Innervation der Kopfseitenorgane der Elritze (Pho.xinus laevis). Z. Morphol. Oekol. Tiere 28: 64-106, 16 figs. Mithel, Manorama. 1964a. The cranial nerves of the si- sorid catfish Bagarius bagarius. Copeia 1964(4): 673-678, 2 figs. . 1964b. The cranial nerves of Mystus seenghala (Sykes). Agra Univ. J. Res. 13(1): 67-78, 7 figs. Narawane, D. D. 1965. Studies on the skeleton, muscula- ture and distribution of nerves in the caudal peduncle and fins of Heteropneustes fossilis Bloch. (Physostomi-Siluri- dae). J. Univ. Bombay 33(5): 64-75, 7 figs. Nelson, Gareth J. 1972. Cephalic sensory canals, pitlines, and the classification of esocoid fishes, with notes on gal- axiids and other teleosts. Am. Mus. Novit. 2492: 49 pp., 23 figs. Norris, Henry Waldo. 1925. Observations upon the pe- ripheral distribution of the cranial nerves of certain fishes (Amia, Lepidosteus, Polyodon, Scaphirhynchus , and Aci- penser). J. Comp. Neurol. 39: 345-432, 12 text-figs., 7 pis. (figs. 13-19). , and Sally P. Hughes. 1920. The cranial, occipital, and anterior spinal nerves of the dogfish, Squalus acan- thias. J. Comp. Neurol. 31(5): 293-402, 53 figs. Pancratz, D. S. 1930. The cranial nerve components in the toadfish (Opsanus tau). J. Comp. Neurol. 50(3): 247-286, 2 pis. Pinkus, Felix. 1894. Die Hirnnerven des Protopterus an- nectens. Morphol. Arbeit. (Jena) 4: 275-346. 7 pis. Ray, Dixie Lee. 1950. The peripheral nervous system of Lampanyctus leucopsarus . J. Morphol. 87(1): 61-178, pis. 1-17. Rosen, Donn E. 1964. The relationships and taxonomic po- FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKI1 53 sition of the halfbeaks, killifishes, silversides, and their rel- atives. Bull. Am. Mus. Nat. Hist. 127(5): 217-268, figs. 1- 23, pis. 14-15. . 1973. Interrelationships of higher euteleostean fishes. pp. 397-513, 129 figs., 4 tables. //;, Greenwood, P. Hum- phry, R. S. Miles, and Colin Patterson. Interrelationships of fishes. Supplement no. 1 to Zool. J. Linn. Soc. 53: 536 pp. , and Colin Patterson. 1969. The structure and re- lationships of the paracanthopterygian fishes. Bull. Am. Mus. Nat. Hist. 141(3): 357-474, figs. 1-74, pis. 52-78. ta- bles 1-8. Saxena, P. K. 1966. Cranial nerves of the common catfish. Clarias batrachus (Linn.). Jpn. J. Ichthyol. 14(1/3): 91-98, pis. 8-12. . 1967. The cranial nerves of the mud ee\, Amphibnous cuchia (Ham.). Acta Anat. 68: 306-320, 3 figs. [Summaries in French and German] . 1969a. The cranial nerves of Nandus nandus (Ham.) and Xenentodon cancila (Ham.). Anat. Anz. 124(2): 142- 155, 3 figs. . 1969b. The cranial nerves of Notopterus notopterus (Pallas). Anat. Anz. 124(2): 198-209, 3 figs. , and Rakesh K. Rastogi. 1968. The cranial nerves of the flat-fish, Cynoglossus bilineatus (Lac). Annot. Zool. Jpn. 41(2): 70-76, 4 figs. Sheldon, R. E. 1914. Paraffine-Weigert methods for the staining of nervous tissue, with some new modifications. Folia Neurobiologica 8(1): 1-28. Springer, Victor G., and Warren C. Freihofer. 1976. Study of the monotypic fish family Pholidichthyidae (Per- ciformes). Smithson. Contrib. Zool. 216: iv + 43 pp., 23 text-figs. Stannius, Hermann. 1849. Das peripherische Nervensys- tem die Fische, anatomisch und physiologisch Untersucht. Rostock. 156 pp., 5 pis. Stensio, E. A. 1947. The sensory lines and derma! bones of the cheek in fishes and amphibians. K. Sven. Vetenskap- sakad. Handl., ser. 3, 24(3): 195 pp., 38 figs. Vasisht. H. S., and I. B. S. Uberoi. 1965. Anatomy of Mystus seenghala (Sykes). IV. Nervous system. Res. Bull. Panjab Univ. (new ser.) 16(1-11): 61-85. Williams, T. W. 1943. A technique for the gross differential staining of peripheral nerves in cleared vertebrate tissue. Anat. Rec. 86: 189-194, 1 pi. Winterbottom, Richard. 1974a. A descriptive synonymy of the striated muscles of the Teleostei. Proc. Acad. Nat. Sci. Phila. 125(12): 225-317, 56 figs. . 1974b. The familial phylogeny of the tetraodonti- formes ( Acanthopterygii: Pisces) as evidenced by their com- parative myology. Smithson. Contrib. Zool. 155: iv + 201, 185 figs. Young, J. Z. 1931. On the autonomic nervous system of the teleostean fish Uranoscopus scaber. Q. J. Microsc. Sci. (new ser.) 74: 491-535. 12 text-figs. 54 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 Abbreviations for Figures A,, A2, A.j — divisions of the adductor mandib- ulae muscle. AA4, AA5 — m. adductores 4,5. ADD OP — m. adductor operculi. AAP2 — m. adductor arcus palatini anterior por- tion. AD HYO — m. adductor hyomandibularis. ADD OP — m. adductor opercularis. AN — anterior narial opening. Anasto w — anastomoses with. AWBl.2,3 — divisions of the mentalis muscle. BB1, BB2, BB3— basibranchials 1, 2, 3. br — branch. br & vis tr of vag — branchial and visceral trunks of nervus vagus. CB1 to CB5— ceratobranchials 1, 2, 3, 4, 5. CIR — a circular, roundish bundle of muscle on top of m. transversus dorsalis. Cor 1 to Cor 6 — branches of ramus ophthalmicus trigeminus to cornea. EM — longitudinal orientation of medial fibers of the sphincter oesophagi. EP1 to EP4 — epibranchial bones 1 to 4. fac — facialis. FR COM — frontal commissure of supraorbital canal. G — nervus glossopharyngeus (n. IX). Gl — branch of m. glossopharyngeus to m leva- tor internus 2. G2 — ramus pretrematicus IX. G3 — branch of IXth to m levator externus 1. G5 — branch of IXth to muscles of gill filaments. G6— branch of IXth to gill rakers. G7 — branch of IXth to m. obliquus ventralis 1. G8 — branch of IXth to m. rectus ventralis 1. GAM — area of attachment of some gill arch muscles. GANG IX — petrosal ganglion of IXth cranial nerve. GG4 — ganglion of 4th vagal branchial ramus. GLR — ramus posttrematicus of IX. H AB — m. hyoidei abductores. H AD — m. hyoidei adductores. HB1 to HB3 — hypobranchial bones 1 to 3. INFOl, 4 — canal neuromasts 1 and 4 of infraor- bital canal. 101 to IOlflb. — branches of ramus buccalis fa- cialis to lateralis organs (or to skin of cheek: these branches actually belong to the r. maxillaris inferioris trigeminus). 102 to I02f — branches of ramus mandibulars trigeminus. I02a — ramus opercularis trigeminus. I02c, I02d, K)2e — to adductor mandibulae muscle of cheek. I02f, I02fl, 2, 3 — to tendinous mucosa near ventral end of maxillary tendon and adja- cent skin. I02f4, a. b — to skin over articular and lip pad at posterior end of lower jaw. I02f5 thru I02f5e — to skin over articular, inter- opercle, angular, anterior end of preopercle and bases of anterior branchiostegal rays. I02f6 thru I02f9 — to skin over ventral surfaces of articular and dentary bones. I02g, I02g2, I02g2a — ramulus mandibularis in- ternus trigeminus (I02g) and branches to m. protractor hyoidei and adjacent skin and mucosa (I02g2) and m. intermandibularis (I02g2a). I02h thru I02j — branches of ramulus mandibu- laris trigeminus externus (I02h) to lower lips, labial cartilage, teeth, and skin near symphysis of lower jaw. 103 and I03a to I03d — ramus maxillaris infer- ioris trigeminus and its branches. IX — nervus glossopharyngeus. LL pore 1. 2. 3. 4 — lateral line canal pores 1 to 4 of dentary. LEI, LE2, LE4 — m. levator externus 1, 2, 4. LEP — m. levator posterior. LGR — lateral row of gill rakers. LI1 to LI3 — m. levator internus 1, 2. 3. Lig I — palatomaxillary ligament. Lig 4 — palatopalatine ligament connecting pal- atine of each side across ascending process of premaxillary. m — muscle. MGR — medial row of gill rakers. MP1 to MP10 — lateralis organs 1 through 10 of mandibulo-preopercular canal. MTC — patch of free lateralis organs between anterior ends of dentaries. NLL — nervus linae lateralis vagi and some of its branches. NLL1 — horizontal septum lateral line nerve of nervus linae lateralis. NLL1 VI— 1st ventral branch of NLL 1. NLL2 to NLL2b — the longitudinal collector lat- eral line nerve (NLL2) and some of its branches. OBD3 — m. obliquus dorsalis 3. OP — m. obliquus posterior. OV1 to OV3 — m. obliquus ventralis 1 to 3. P2 — branch of r. palatinus. FREIHOFER: CRANIAL NERVES OF POLYCENTRVS SCHOMBVRGKll 55 PCI — m. pharyngoclavicularis internus. PCE — m. pharyngoclavicularis externus. PCL — vertical row of free lateralis organs in front of preopercle. PHI to PH3 — infrapharyngo-branchials 1 to 3. PIV — pharyngo-intestinal trunk of nervus va- gus. PN — posterior narial opening. POl — 1st lateralis organ of postorbital section of cephalic lateralis canal system. PPR — posterior palatine ramus. PR HY — m. protractor hyoidei. PRP — m. protractalis pectoralis. PRPE — branch of ramus opercularis vagi to m. protractor pectoralis. PT1 — lateralis organ of posttemporal canal. QTAW — quadrate tendon of mentalis muscle. r — ramus. RCOM — m. rectus communis. r com v — ramus communicans from Gasserian ganglion to truncus hyomandibularis. RETD — m. retractor dorsalis. r hyo — ramus hyoideus RIN — r. intestinalis and r. cardiacus vagi. RLA-OP — orbito-pectoral branch of ramus lat- eralis accessorius (recurrent facial nerve). RLA-PD — parieto-dorsal branch of ramus lat- eralis accessorius. r mand fac — r. mandibulars facialis. r mand ext fac — ramus mandibulars externus facialis. r mand int fac — ramus mandibulars internus fa- cialis. r mand trig (102) — ramus mandibularis trigemi- nus. r op 1 thru r op 3b — branches of ramus oper- cularis vagi to skin and mucosa of opercle and part of subopercle. r oper fac — ramus opercularis facialis. r op sup fac — ramus opercularis superficialis fa- cialis. r oph sup fac — ramus ophthalmicus superficialis facialis. r ophth sup tri — ramus ophthalmicus superfici- alis trigeminus. r oper vagi — ramus opercularis vagi. R SUPR 1 to R SUPR Id— branches of lateralis portion of ramus supratemporalis vagi with some general cutaneous fibers. R SUPR 2 and R SUPR 2a— portion of ramus supratemporalis vagi containing in part the rami cutanei dorsalis vagi. RSV — ramus supratemporalis vagi. RV1, RV4, RV5— m. rectus ventralis 1, 4, and 5. SIR — esophageal ramus of 4th vagal branchial ramus. SOI to S05 — canal neuromasts 1 through 5 of supraorbital canal. SORB 2 to S0RB2b— branches of truncus su- praorbitalis to meninges, skin, and free lat- eralis organs above orbit. SORB3— joins RLA-PD intracranially. SORB4 — branch of ramus ophthalmicus super- ficialis facialis. S0RB5 — branch of r. ophth. sup. trigeminus to skin dorsal to orbit. SORB6 to S0RB7 A— branches of r. ophth. sup. trigeminus to skin of snout. SORBS and SORB9— branches of r. oph. sup. facialis to 1st and 2nd supraorbital canal organs of frontal bone. SORB 10, SORB1 1-1 la— branches of r. oph. sup. trigeminus to skin and free lateralis organs near nasal canal and to lateralis or- gan of nasal canal. ST1 — dorsalmost lateralis organ of supratem- poral canal. STL — vertical line of free lateralis organs in front of supratemporal canal. SYM TR — sympathetic trunk. T — tendon. TA1, TA3 — tendons of A, and A3 divisions of m. adductor mandibulae. TA W/33 + TA2— tendon of A2 and of AW/33 di- visions of mentalis muscle. TD1. TD2 — m. transversus dorsalis 1 and 2. TH — truncus hyomandibularis. TH1 — posterior palatine ramus. TH2, TH3 — anterior and posterior parts of ra- mus opercularis profundus facialis. TH4 — ramus opercularis superficialis facialis. TH4AA, TH4BB, TH4BB1, TH4BB2— branch- es of r. oper. sup. fac. innervating lateralis organs on opercle and subopercle. TH5 — to canal organ #11 of mand.-preopercular canal. TH6 — to skin between opercle and interopercle. TH7 — anastomoses with cutaneous branch from IOlc. TH8— to canal organ #10 of mand.-preopercular canal. TH9. TH9A. TH9B. TH9Bla-le. TH9B0, TH9B02-05. TH9C. TH9C2. TH9D-TH9F. TH10, TH10A-TH10B4, TH 11— ramus hy- oideus and its branches. 56 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 THI2 — ramus mandibularis internus. TH12A— TH12C — to mucosa of anterior part of palate and to ectopterygoid teeth. TH 13, TH 13 A-B, TH 14-15— branches of ramus hyoideus. TH16 — branch of ramus hyoideus anastomosing with I02f. TH 17-TH 17a, TH 18— lateralis branches of r. mand. fac. to mand. preopercular canal. TH18a — branch of combined r. mand. tri. & r. mand. fac. to mucosa on medial side of den- tary. TH19, TH19a-TH19a4,TH19b-TH19b4,TH19b 4a — branches of combined r. mand. tri. and r. mand. fac. to skin, taste buds, gums of teeth, and mucosa of anterior part of lower jaw. TH20 — lateralis branch of r. mand. facialis to mandibulo-preopercular canal. TH20a-TH20c — to skin on ventral surface of dentary. TH21, TH21a, TH22— lateralis and cutaneous branches of combined r. mand. tri. & r. mand. fac. to mandibulo-preopercular canal and to skin. TH23, TH23a-b, TH24, TH24a, TH24b, TH25— lateralis and cutaneous branches of com- bined r. mand. tri & r. mand. fac. tr — truncus. TS1 — canal neuromast of first (and only) truncus lateral line scale. TV4, TV5 — m. transversus ventralis of the fourth and fifth branchial arches, respec- tively. VI — 1st vagal branchial ramus. VI is the prefix to all branches of this first ramus. VIA — branch of 1st branchial ramus to levator externus 2. V1B — branch of 1st vagal posttrematic branchial ramus to gill rakers. VIC — to m. obliquus ventralis 2. VIE — to 1st epibranchial gill rakers. VIP — pharyngeal ramus of 1st vagal pretrematic branchial ramus. V1PO — 1st vagal posttrematic branchial ramus. V1PR — 1st vagal pretrematic branchial ramus. V2A — branch of 2nd vagal posttrematic bran- chial ramus to m. levator posterior. V2B — branch of 2nd vagal posttrematic bran- chial ramus to m. levator externus 4. V2C — branch of 2nd vagal pretrematic branchial ramus to m. obliquus dorsalis III and m. transversus dorsalis 2. V2D — branch of 2nd vagal pretrematic branchial ramus to m. transversus dorsalis 2. V2E — branch of V2P to ceratobranchial gill rak- ers. V2F — branch of 2nd posttrematic vagal bran- chial ramus to gill rakers. V2G — branch of 2nd posttrematic vagal bran- chial ramus to m. rectus communis. V2H — branch of 2nd posttrematic vagal bran- chial ramus to m. rectus ventralis 4. V2J — branch of 2nd vagal branchial posttrema- tic ramus to m. obliquus ventralis 3. V2P — pharyngeal ramus of 2nd vagal pretrem- atic ramus. V2PO — second vagal posttrematic branchial ra- mus. V2PR — 2nd vagal pretrematic branchial ramus. V3A — branch of 3rd vagal branchial ramus to m. retractor dorsalis. V3B — branch of 3rd vagal branchial posttrema- tic dorsalis ramus to gill rakers. V3E — gill raker branch of pharyngeal ramus of 3rd vagal branchial ramus. V3P — pharyngeal ramus of 3rd vagal branchial ramus. V3PO — 3rd vagal posttrematic branchial ramus. V3PR — 3rd vagal pretrematic branchial ramus. V4A — to mucosa of roof of posterior end of pharynx. V4B — branch of 4th vagal posttrematic branchi- al ramus to m. obliquus posterior and ad- ductor 5. V4C — branch of V4PO to teeth and mucosa of 5th ceratobranchial. V4D — branch of V4PO to m. transversus ven- tralis IV. V4E — branch of V4PO to pharyngoclavicularis externus and internus muscles. V4PO — 4th vagal posttrematic branchial ramus. V4PR — 4th vagal pretrematic branchial ramus. X — nervus vagus. la to lh — branches of ramus maxillaris trigem- inus (coursing in ramus buccalis facialis) to skin over cheek and part of preopercle. 3b to 3g — branches of ramus buccalis innervat- ing free lateralis organs on orbitals and lach- rymal. 3 BC — branch of 3rd vagal posttrematic bran- chial ramus to m. adductores 4. 3 BD — branch of 3rd vagal posttrematic bran- chial ramus to m. transversus ventralis 4. fREIHOFER: CRANIAL NERVES OF POLYCENTR US SCHOMBURCK11 r maxillaris (103) 102b inferioris v COR 6 r t 101c I01d I01d I01e I01f I01f 1 I01f a I01f b r palatinus fac IC3c 1 SORB 2b 101 101b 10 I03d r palat COR 4 r opercularis trigeminus (I02a) r mandibulars trigeminus (102) Figure 1. Polycemrus schomburgkii . Lateral view of branche- of infraorbital trunk to snout and suborbital regions. See text and list of abbreviations. 58 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBVRGKI1 ™ 4AA r com V TH 5\ r op sup fac (TH 4) tr hyomandibularis (TH) r opercularis facialis (TH2) TH 7 TH 10(rbuccalis accessorius) TH 10B TH11 TH 10B1 H 9B 1a H 9B 1b H 9B 1c H 9B 1d H 9B 1e TH 9B 02 TH 9B 1e TH 9B 02 TH 14 TH 9B 1e TH 15 TH 9C TH 10B 2 is internus (TH 12) mam TH 16 TH 10B 3 anasto w I02f TH 10B 4 anasto w I02f5 b TH 9B 1e TH 9B 05 TH 17 TH 9B 1e r hyoideus Figure 2. Polycentrus schomburgkii. Lateral view if branches of truncus hyomandibularis. 60 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII 61 S0RB 7 SORB 8 S0RB 7A C°R 2 SORB 5 \ L RLA-OP RAMUS OTICUS Tr supraorbitalis FR COM SORB 6B SORB 6C R OPH SUP FAC R OPH SUP TRI Figure 3. Polycentrus schomburgkii . Oblique view of supraorbital trunk looking towards roof of orbital cavity. TH3 PREVOM LOP PARASPHENOID NLL PALATINE tr R PALATINUS ^SYM TR V \\ # \\ lx 7^XUf G2 GANG IX SYM TR TH1 PSEUDOBRANCH Figure 4. Polycentrus schomburgkii . View looking dorsally showing branches of truncus hyomandibularis and glosso- pharyngeal nerves to palate and posterior floor of cranial area. 62 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 NLL2 RSUPRlc RSUPRlb RLA-PD NLL2b NLL1 NLL2a RLA-OP NLL2 RSUPRi SUPR 2 SUPR 1 R SUPRATEMPORALIS VAGI ROTICUS TR INFRAORBITALS Figure 5. Polycentrus schomburgkii . Lateral view of main divisions and some branches of supraorbital trunk, lateral line nerves and supratemporal ramus of vagus nerve to dorsoposterior side of head. r mandibulars trigeminus (102) Figure 6. Polycentrus schomburgkii. Lateral view of cheek area showing pattern of innervation to adductor arcus palatini and adductor mandibulae muscles. FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKU 63 RAMUS MANDIBULAR IS INTERNUS FACIALIS RAMUS MANDIBULARS TRIGEMINUS (102) ARTICULAR- RAMUS MANDIBULARS EXTERNUS TRIGEMINUS RAMUS MANDIBULARS EXTERNUS FACIALIS angular DENTARY RAMUS MANDIBULARS FACIALIS RAMULUS MANDIBULARS INTERNUS TRIGEMINUS (I02G) Figure 7. Polycentrus schomburgkii . Medial view of lower jaw showing innervation to mentalis division of adductor mandibulae muscle. 102 j TH19b2 ,02i\ J-1-^ TH!9b1 TH 19b3 ^^I02g2 TH 20c TH21 mand f ac ♦ 102 g eckel s cartilage ramulus mand ext tri (I02h) Figure 8. Polycentrus schomburgkii. Dorsal view of branches of ramus mandibularis trigeminus and of r. mand. facialis to anterior half of lower jaw. 64 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 LL pore 3 TH 20c TH24 TH24a^ LL pore1^ TH24b TH25 I02 g2 I02f8 r man tri (I02) I02f ^TH16 ^=V|02f5 ^^^^r man fac ?M^z-- I02f5b - I02 f5c myoseptum I02f5a I02f6 myoseptum I02f7 Figure 9. Polycentrus schomburgkii. Ventral view of branches of ramus mandibularis trigeminus and r. mand. facialis to lower jaw. TH19a2 102 f TH19 ectopterygoid I02 h / ,Q2h TH 19b1 I02i TH19a1 TH23- TH 24 TH25"" 102 g2a TH 22a TH19b nd tri(l02) 02f1 r mand int fac -quadrate r mand ext fac angular articular TH 17a x Meckel's cartilage I H 20a \dentary xTu 10 TH20c ™18 TH 20b canal pore I02g2 TH19b4 Figure 10. Polycentrus schomburgkii. Medial view of lower jaw showing some innervation of dentary region. FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII us D ._ 2 2 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 truncus hyomandibularis r mandibularis facialis TH 9A r mand int fac r mand ext fac TH 9B I02g2 r oper vagi TH 8 r hyoideus (TH 9) TH 9B 1a TH 9B 03 TH 9B 02 Figure 13. Polycentrus schomburgkii. Medial view of hyoid arch and opercular bones showing distribution of ramus hyoideus. SUPERIOR RECTUS NERVUS OPTICUS (Nil) SUPERIOR OBLIQUE INFERIOR 08L INTERNAL RECTUS CILIARIS BREVIS NERVUS TROCHEARUS IN. IV I CILIARIS LONCIJS CILIARY GANGLION GASSERIAN GANGLION PROFUNDUS GANGLION RADIX PROFUNDUS NERVUS OCULOMOTOR IUS IN. Ill I TRUNCUS CILIARIS PROFUNDUS NERVUS ABDUCENS IN. VI ) INTERNAL RECTUS RADIX LONGUS EXTERNAL RECTUS INFERIOR RECTUS Figure 14. Polycentrus schomburgkii. Medial view of eyeball and eye muscles showing distribution of cranial nerves III, IV, and VI, and ramus profundus. FREIHOFER: CRANIAL NERVES OF POLYCEMTRUS SCHOMBURGKII (.7 ciliaris longus "ciliaris brevis Figure 15. Potycentrus schomburgkii . Medial view of eyeball showing branches of ciliaris longus and ciliaris brevis of radix profundus. cor 2 cor 1 to skin cor 6 cor 5 cor 4 Figure 16. Polycentrus schomburgkii . Lateral view of eyeball showing branches of supraorbital and infraorbital trunks innervating skin and cornea. 68 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO 128 ST1 INF01 MP1 Figure 17. Polycentrus schomburgkii. Lateral view of head showing distribution of free lateralis organs (open circles), canal neuromasts (paired triangles), and canal pores (black circles). FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII 69 EUDOBRANCH DORSAL HYPOHYAL VENTRAL HYPOHYAL Figure 18. Polycentrus schomburgkii. Lateral view of gill arches and pectoral girdle showing associated gill arch muscles. Anterior to right. -(I OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 R OPER VAGI V2J Figure 19. Polycenirus schomburgkii . Lateral view of gill arches showing innervation. FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGK1I 71 latera medial gill fila G5 al gill raker G6 of 1st vagal branchial nerve Figure 20. Polycentrus schomburgkii . Lateral view of ceratohranchial section of first gill arch showing details of innervation of branches of glossopharyngeal nerve. FREE LATERALIS ORGANS NLLla NLL1 NLL1 V1 Figure 21. Polycentrus schomburgkii . Lateral view showing trunk lateral line nerves. 72 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 II. LEVATOR OPERCUL PALATINE MAXILLAR RAMUS MANDIBULARS TRIGEMINUS 1102 I Figure 22. Polycentrus schomburgkii . Lateral view of head showing opercular and superficial cheek muscles and jaw ligaments. /Z^RAMUS MANDIBULARS INTERNUS RAMUS MANDIBULAR IS EXTERNUS INTERMANDIBULARIS MUSCLE Figure 23. Polycentrus schomburgkii. Medial view of jaws and associated bones showing tendons of jaw muscles and mentalis (A„) muscle. FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII 73 1NM -JJ m. INTERMANDIBULARIS MECKEL'S CARTILAGE RAMUS MANDIBULARIS TRIGEMINUS Figure 24. Polycentrus schomburgkii . Medial view of jaws showing insertion of adductor mandibulae muscles and tendons. HYOIDE! A HVOIDEI ABDUCTORES MUSCLE Figure 25. Polycentrus schomburgkii. Medial view of opercle and hyoid arch showing hyohyoideus muscle. 7-4 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 MESOPTERYGOID ADDUCTOR ARCUS PALATINI POSTERIOR PORTION HYOMANDIBULAR BONE PREOPERCLE AREA OF ORIGIN OF SOME GILL ARCH MUSCLES m. ADDUCTOR HYOMANDIBULARIS m, DILATATOR OPERCULI m. LEVATOR OPERCULI PSEUDOBRANCH FIRST INFRAPHARYNGOBRANCHIAL NERVUS VAGUS ( N. X ) BAUDELOT'S LIGAMENT SYMPATHETIC TRUNK NERVUS GLOSSOPHAKYNGEUS ( N. IX) OTIC BULLA PARASPHENOID TRUNCUS HYOMANDIBULARIS Figure 26. Polycentrus schomburgkii. Ventral view of palate and rear of cranium showing muscles of palate, hyomandibular. and opercle. RANCHIOSTEGAL RAY HYOIOEI ABDUCTORES MUSCLE Figure 27. Polycentrus schomburgkii. Ventral view of protractor hyoidei muscle, tip of lower jaw. and part of hyoid arch. FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII 75 nervus trochlears (l\l. IV corpus cerebelli eminentia granularis nervus auditorius ( N. VIII ) nervus linae lateralis NERVUS VAGUS ( N. X olfactory organ nervus olfactorius ( N. I ) m. superior oblique exit from cranial cavity cut end of anterior semicircular cana cristae medulla oblongata Figure 28. Polycentrus schomburgkii. Dorsal view of brain and nerve roots. 76 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 .£. FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKIl 77 > — CD 7S OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128 1ST9 MBI. WHOI LIBRARY WH 1TG2 Y