The Trigeminal Nerve in the Baboon' RAYMOND F. GASSER AND D. MILLER WISE Department of Anatomy, Louisiana State University Medical Center, New Orleans, Louisiana 70112 ABSTRACT The dehitive course, relations, branches and communications of the extramedullary part of the trigeminal nerve in baboons are described and illustrated. The nerve was dissected in five animals and the location of all related parasympathetic ganglia was verified microscopically. Variable branching patterns were observed in some areas of the nerve field. Comparisons are made with other primates including man. The investigator using the baboon for research purposes must be aware of the differences that exist between this animal and man. Only by knowing the detail in the anatomy of the laboratory animal can one interpret changes produced by experimental techniques. In recent years, the baboon has been found to be an excellent research animal since it responds to many drugs in a manner similar to man, contracts many similar diseases and is hardy in captivity where it adjusts and reproduces with little difficulty. Additional information on the anatomy of this primate is badly needed. An understanding of the arrangement of the trigeminal nerve of this animal is basic to present and future studies on the head region. Gasser and Hendrickx ('69) reported on the embryonic development of the nerve in baboons but information on its definitive arrangement is scant and fragmentary. A description of the frontal and lacrimal branches of the ophthalmic division was given by Lacroix ('27). Ashton and Oxnard ('58) reported briefly on the branching pattern of the maxillary division. Communications between the facial and trigeminal nerves were delineated by Bowden, Mahran and Godding ('60) and Gasser and Hendrickx ('67) described their embryonic development. Swindler ('67) illustrated some of the cutaneous branches along with other facial structures. A survey of the literature on the peripheral nervous system of Papi0 was made by Hill ('70) which includes some studies on the trigeminal nerve. This paper presents the definitive course, relations, branches and communications ANAT. REC., 172: 511-522. of the extramedullary part of the trigeminal nerve in baboons. This nerve is the primary route by which sensations from the head region reach the brain and it brings motor impulses to the muscles of mastication as well as several other muscles. It is essential for the distribution of the autonomic innervation of cranial viscera. The location of the four, closely associated parasympathetic ganglia is included. Some comparisons are made with the arrangement of the nerve in man and other primates. MATERIALS AND METHODS The nerve was dissected in five heads of the species, P a p b cynocephalus. Three of the specimens were adults; two were immature forms one to two years old. After sacrifice, they were perfused with and stored in 10% formalin. The arteries of one specimen had been injected with red latex. The arrangement of the dissected nerve was recorded on drawings made from photographs of the specimens. Tissue that was suspected of containing ganglion cells was processed for microscopic examination using hematoxylin and eosin or toluidine blue stains. The location of all related ganglia was verified microscopically. OBSERVATIONS The arrangement of the trigeminal nerve rootlets and ganglion will be described together but each division of the nerve with Received Aug. 12, '71. Accepted Oct. 26, '71. 1 Supported by National Institute? of Health FR-5376 and the Edward G. Schheder Educaf%% Foundation. 511 512 RAYMOND F. GASSER AND D. MILLER WISE its branches and associated ganglia will be described separately. Ophthalmic division This division is the smallest of the three and courses craniomedially from the ganglion through the superior orbital fissure (fig. 1A). It gives off a meningeal branch and then divides into three major branches as i t enters the orbit. Rootlets and ganglion The sensory rootlets course from the lateral aspect of the pons to the ganglion and are approximately 5 mm in length (fig. 1A). The motor root leaves the pons caudal and medial to the sensory rootlets and passes obliquely across the caudal as- Branches 1. A small meningeal (tentorial) branch pect of the sensory rootlets and ganglion to join the mandibular division. The gan- arises from the division just proximal to glion has a semilunar shape with the three the superior orbital fissure. This filamentdivisions arising at its periphery. It mea- ous nerve terminates in the tentorium sures approximately 5 x 10 mm. cerebelli after a short craniolateral course. 1. Cerebellum 2. Trochlear n. 3.Cerebral peduncle 4. Pons 5 posterior clinoid processes 6. oculomotor n. 7. Internal c a r o t i d a. 8.0ptic chiasma 9.Trigeminal n. r o o t (motor r o o t d o t t e d ) 10. Trigeminal ganglion 11. Optic n. 12. Frontal n. 13. Levator, pajpebrae superioris m. 14. Superior r e c t u s m, 15. Ophthalmic n. 16. Abducens n. 17. Meningeal brs. 18. Mandibular n 19. Maxillary n. 2Q Lacrimal n. 21. Nasociliary n. 22. Ciliary ganglion 23 Glandular br of lacrimal n. 24. Short.ciliary nn. 25. Superior oblique m. 26. ODhthalmic a. o r brs. 2% Medial rectus m. 28. Anterior ethmoidal n n. 29. Olfactory bulb 30. L a t e r a l rectus m. 31. Lacrimal gland 32. Bulb of eye 33. Lnftatrochlear nn. 34 Supratrochlear n. 35. Supraorbital nn. 36,Zygomatic brs. of lacrimal n. Fig. 1A Cranial view of the orbit and middle cranial fossa showing the relationships and branches of the trigeminal ganglion and its ophthalmic division. Fig. 1B Cranial view of the more detailed relationships around the ciliary ganglion. BABOON TRIGEMINAL NERVE 2. The frontal nerve is the largest branch. It travels rostrally in the craniomedial part of the orbit in close association with the trochlear nerve. As it approaches the orbital brim it divides into two supraorbital nerves (lateral and medial) and a more medial suprcotrochlear nerve. All of these nerves emerge from the orbit in a groove on the frontal bone. The supraorbital nerves course cranially for a short distance over the supraorbital torus and divide into many fine cutaneous rami in the intermediate portion of the frontal region (figs. 4, 5). The supratrochlear nerve is more medial but also takes a cranial direction to the skin of the frontal region. 3. The lacrimal nerve passes ventrolaterally on the lateral aspect of the lateral rectus muscle (fig. 1A). At the proximal part of the muscle it divides into a medial, glandular branch and a lateral, zygomatic branch. The glandular branch proceeds to the lacrimal gland. The larger zygomatic branch courses ventrally in the craniolateral aspect of the orbit. It emerges from the orbit through a canal located at the junction of the zygomatic and frontal bones, then divides into branches that course to the skin in the lateral portion of the frontal region and ventral portion of the temporal region (figs. 4, 5 ) . One of its branches occasionally communicates with the facial nerve in the infraorbital region. 4. The nasociliary nerve courses ventrally for a short distance and is adjacent to the abducens nerve (fig. 1). It then turns medially just caudal to the superior rectus muscle and is closely associated with the ophthalmic artery and orbital fat. The proximal part of the medially coursing segment gives rise to a fine branch to the ciliary ganglion. The nerve then proceeds ventromedially between the superior oblique and medial rectus muscles where it usually divides into two anterior ethmoidal nerves and two or three fine infratrochlear nerves. The anterior ethmoidal nerves course medially through the ethmoid bone to the cribriform plate where they reunite in the dura into a single bundle beneath the olfactory bulb. The common nerve enters the nasal cavity through the cribriform plate and immediately divides 513 into medial and lateral internal nasal branches (fig. 3). Both branches course toward the external nares in the roof of the nasal cavity close to the nasal septum. The lateral branch passes through the junction region of the nasal bone with the nasal cartilage to become the subcutaneous external nasal branch. This branch innervates the skin over the cartilagenous portion of the nose. The infratrochlear nerves emerge from the orbit by passing cranially over the most medial portion of the orbital brim to the skin on the root of the nose and adjacent frontal region at the midline (figs. 4, 5). Ciliary ganglion The ganglion lies between the lateral rectus muscle and the optic nerve in a position ventral to the ophthalmic artery (fig. 1). It measures approximately 1 X 2 mm. The lower division of the oculomotor nerve sends two small branches to the ganglion and the nasociliary and abducens nerves each give a small communication. Two very fine nerve filaments arise from fascicles around the ophthalmic artery branches that course to the medial portion of the bulbus oculi. These Haments communicate with the ganglion by passing above and below the optic nerve (fig. 1B). Two fascicles arise from the ventral aspect of the ganglion. Each subdivides into two finer fascicles ( s h t ciliary nerves) that enter the dorsal aspect of the bulbus oculi above and below the optic nerve. Tiny branches of the ophthalmic artery accompany the short ciliary nerves throughout their course. Maxillary division This division courses ventrally and slightly medially from the trigeminal ganglion to emerge from the cranial cavity through the foramen rotundum (fig. 1A). It then travels in a cranioventral direction across the pterygopalatine fossa to the infraorbital canal where it continues as infraorbital nerves in the floor of the orbit (fig. 2). In the fossa, the maxillary division is in close association with the terminal branches of the maxillary artery. Branches 1. A tiny meningeal branch arises close to the trigeminal ganglion and travels in a 514 RAYMOND F. GASSER AND D. MILLER WISE 1. Pterygoalar foramen 2. Mandibular n. 3. Meningeal br. 4. Auriculotemporal n. 5.Chorda tympani n. 6. N. t o masseter . Deep temporal nn. 10. Zygomatic n. 11. Pterygopalatine ganglion 12. Nasopalatine n. 13. Maxillary a. 14. Lateral pterygoid m. 15. Deep temporal n. 16. Temporalis rn. segment 17, Buccal n 18. N. t o lateral pterygoid 19. Inferior alveolar n. 20.N. t o medial pterygoid 21. Medial pterygoid m. 23 Mand ib I e 24. Lingual n. 25.Submandi bular ganglion 26.Mylohyoid m. 27.Ant belly digastric rn. 28 Buccinator m. 29.Buccal pouch 30.Mental nn. 31. Incisive br. Fig, 2 Lateral view of the arrangement of the more proximal portion of the maxillary and mandibular divisions. caudolateral direction to the dura mater (fig. 3). 2. The zygomatic nerve is variable in its course and branching pattern. In one of the specimens, the nerve originates from the division in the floor of the orbit, passes ventrolaterally into a canal in the zygomatic bone and emerges from the bone by way of a foramen (zygomatic) to innervate the skin lateral and caudal to the orbit (fig. 4). In another specimen, the nerve divides near its origin into two, very small branches. One of the branches courses through the lateral wall of the orbit to the ventral part of the temporal fossa where it joins the other branch that passes laterally through the pterygomaxillary fissure. The common nerve innervates a small area of skin lateral and caudal to the orbit (fig. 5). In this arrangement, a foramen is not apparent on the outer surface of the zygomatic bone. A third arrangement encountered is similar to that described for man with the nerve dividing into zygomaticofacial and zygomaticotemporal branches. The facial branch courses 515 BABOON TRIGEMINAL NERVE 1. L,esser petrosal n. 2. N. t o tensor tympani 3.Otic ganglion 4. Mandibular n. 5,,N t o levator veli palatini 6.N. t o medial pterygoid I?. Inf. alveolar n. 7. Communicating br: 12. Muscular brs. 8. Auriculotemporal n. 13 Tendon of digastric m. 9.Chorda tympani n. 14. Submandibular gland 10.N. t o mylohyoid 15. Facial a. 16. Styloglossus rn. 17 Submandibular ganglion 18 Lingual n. 19. Hyoglossus rn. 20. Hypoglossal n. 21. Sublingual gland 22 Su brnandibular duct 23 Mylohyoid m. 24..Ant. belly digastric m. 2,Ei:Sublingual a. 2G. Tongue 2'7. Mandible 2r3.Zygomatic n. 23 Med. pterygoid 30. Maxillary n. 31. Meningeal bt: 3.2. Pharyngeal n. m. 33. N. of pterygoid canal 34. Pterygopalatine ganglion 35.Nasopalat ine n. 36.Orbital brs. 37;lnfraorbital nn. 38.Lat nasa 1 brs. 39.Post. sup. alveolar n. 40. Lesser palatine nn. 41. Ant. sup alveolar n. 42 Mid. sup. alveolar n. 43. Greater palatine n. 44. Incisive brs. 45. Ant. ethmoidal nn. 46.Med. int. nasal br: 47. Lat. i n t nasal br: 4 8 Ext. nasal br: Fig. 3 Lateral view of the arrangement of the more intermediate portion of the maxillary and mandibular divisions and the anterior ethmoidal branches of the ophthalmic division. through the zygomatic bone and emerges by way of a prominent foramen. The temporal branch travels through the lateral wall of the orbit, across the temporal fossa to the skin of the ventral part of the temporal region. The size of the cutaneous field supplied by the zygomatic nerve appears to be inversely proportional to that supplied by the zygomatic branch of the lacrimal nerve. These two nerves usually communicate with one another. 3. The pteTygopaEatine nerves are short, medially directed fascicles that terminate in the pterygopalatine ganglion (fig. 3 ) . 4. The posterior superior alveolar nerve arises from the division in the pterygopalatine fossa. As it courses caudally through the pterygomdary fissure it di- 516 RAYMOND F. GASSER AND I>. MILLER WISE vides into two or more small rami. After a short course, the rami enter minute foramina in the dorsal part of the maxilla and innervate the dorsal maxillary teeth. 5. The division terminates as five or six large fascicles which travel through the floor of the orbit as infraorbital nerves. These nerves become subcutaneous by passing from the maxilla through approximately six foramina that vary in size and location. Peripheral branches of the nerves course to the skin of the lower eyelid, upper lip and lateral snout (figs. 4, 5). Plexuses are present in the infraorbital and buccal regions that communicate with the buccal branches of the facial nerve. Two superior alveolar nerves (anterior and middle) arise from the infraorbital nerves and course through canals in the maxilla to the rostral maxillary teeth (fig. 3). down the septum to the incisive foramen through which it travels to communicate with the terminal branches of the greater palatine nerves just behind the incisor teeth. lateral nasal d. Several posterior branches arise from the ganglion and innervate the mucosa on the dorsal part of the large inferior concha and adjacent areas of the nasal cavity. e. A tiny pharyngea2 ramus travels in a dorsal and caudal direction from the ganglion to the roof of the nasopharynx. f. Several fine orbital branches course cranially from the ganglion through the inferior orbital fissure to join the orbital nerves passing through the superior orbital fissure. g. The nerve of the pterygoid canal enters the dorsal aspect of the ganglion after passing through a bony canal. Pterygopalatine ganglion Mandibular division The ganglion is housed in the pterygoThis division proceeds caudally and palatine fossa that is dorsal to the maxilla, caudal to the orbit and lateral to the dorsal laterally from the trigeminal ganglion to emerge from the cranial cavity by way of part of the nasal cavity (figs. 2, 3). the foramen ovale (fig. 1A). Very shortly Branches i t divides into ventral (pars anterior) and a. One or two greater palatine nerves dorsal (pars posterior) portions just lateral course in a caudal and ventral direction to the auditory tube. The ventral portion through a bony canal to reach the dorsal passes through a bony foramen (pterygopart of the hard palate. They emerge from alar) in the lateral pterygoid plate to the the canal by way of a large foramen at the infratemporal fossa (fig. 2). Here, it dijunction of the maxillary and palatine vides into nerves primarily to the muscles bones. The nerves branch repeatedly deep of mastication. The larger dorsal portion to the mucosa on the roof of the oral cavity travels caudally and laterally along the as they travel toward the incisor teeth. dorsal border of the lateral pterygoid plate. Fine rami are given to the mucosa of the palate and the lingual side of the maxillary Branches gingiva before the terminal branches com- Undivided portion municate with the nasopalatine nerve near 1. A filamentous meningeal branch the incisive foramen. b. A pair of much smaller lesser palatine arises before the division leaves the cranial nerves proceeds caudally from the ganglion cavity and travels laterally to the dura in a groove where the maxillary and mater (fig. IA). 2. The medial pterygoid nerve courses sphenoid bones join. The nerves may either pass through a bony canal to reach the from the deep aspect of the division in soft palate or they course outside the bone close association with the otic ganglion. just lateral to the junction of the palatine It is small and arises near the point where the division bifurcates into its two portions and maxillary bones. c. The nasopalatine nerve arches me- (figs. 2, 3). After a short caudoventral dially from the ganglion, deep to the mu- course from the foramen ovale it sends one cosa in the dorsal part of the nasal cavity, branch into the lateral surface of the meto the nasal septum. It passes obliquely dial pterygoid muscle and a more medially BABOON TRIGEMINAL NERVE 517 8. The inferioT alveolar nerve is one of two terminal branches of the dorsal portion. It proceeds in a caudal and ventral Ventral portion direction on the lateral surface of the 3. The masseteric nerve is the first medial pterygoid muscle into the mandibubranch of the ventral portion and travels lar foramen (figs. 2, 3). Prior to entering laterally, cranial to the lateral pterygoid the mandible, it gives off the mylohyoid niuscle and mandibular notch to enter the nerve which, after coursing in a groove on deep surface of the masseteric muscle the medial surface of the mandible, divides (figs. 2, 4). into several branches. The mylohyoid nerve 4. There are usually three deep temporal not only innervates the mylohyoid and annerves which vary in their relative size terior (ventral) belly of the digastric and point of origin. All three may arise muscles but it also sends branches to the completely from the masseteric nerve or medial pterygoid muscle and the submancompletely from the parent stem of the dibular gland and ganglion. The inferior ventral portion or from a combination of alveolar nerve sometimes divides into two both (fig. 2). They originate near the fascicles prior to entering the mandible. cranial aspect of the lateral pterygoid mus- Within the mandible it breaks up into cle and travel to the deep side of the tem- several fascicles that communicate with .poralis muscle. each other and send rami to the mandibu5. As the ventral portion passes deep to lar teeth. The plexus usually gives rise to the lateral pterygoid muscle it sends a four or five mental nerves (figs. 2, 4, 5). small lateral pterygoid nerve into the deep The size and position of these nerves vary surface of the muscle. but their rami regularly course to the skin 6. After the last motor nerve arises, the of the chin and lower lip and the mucosa ventral portion of the division passes on the inner aspect of the lip. The marthrough the upper head of the lateral ginal mandibular branch of the facial pterygoid muscle as the buccal nerve. It is nerve is closely associated with the mental usually a single bundle that travels in a nerves but no large communications are caudal and ventral direction through part apparent. After the mental nerves are given of the temporalis muscle to the buccal off, the inferior alveolar nerve continues region. However, it can separate into two within the mandible to the incisor teeth as parts which course around portions of the the incisive branch. temporalis muscle and then reunite (fig. 2). 9. The other terminal branch of the dorShortly after it emerges from the muscle, sal portion, the lingual nerve, takes a it sends rami superficially to the skin and course that arches caudally and ventrally deeper rami through the buccinator mus- on the lateral surface of the medial pterycle to the mucosa of the cheek and buccal goid muscle, sometimes passing through pouch. part of the muscle (figs. 2, 3 ) . The chorda tympani nerve emerges from the skull Dorsal portion through a prominent petrotympanic fissure 7. The first branch of the dorsal portion and proceeds medial to the auriculotemis the auriculotemporaE nerve which travels poral and inferior alveolar nerves to join caudolaterally, deep to the lateral pterygoid the lingual nerve. After passing the medial muscle (figs. 2, 3). It then passes dorsally, pterygoid muscle, the lingual nerve courses deep to the condyle and neck of the man- medially and sends several communicadible. From this location it takes a cranio- tions to the submandibular ganglion. Conlateral course through the parotid gland tinuing ventrally, it spirals around the to become subcutaneous in front of the submandibular duct to pass medial to the auricle. It communicates with the otic gan- sublingual gland. After branches are given glion and the facial nerve and sends to the gland, the nerve divides into many branches to the temporomandibular joint rami which course to the mucosa on the body of the tongue. Several of the more and auricle. directed branch to the tensor veli palatini muscle. 518 RAYMOND F. GASSER AND D. MILLER WISE I. Auriculotemporal n. 2 Superficial temporal a. 3 P a r o t i d gland 4 Facial n. 5. Temporal br. (VII) 6. Zygomatic br (VII) 11. Supraorbital nn. 12. Supratrochlear n. 13 l n f r a t rochlear nn. !4. Palpebral br. 25. Infraorbital n n B plexus 6 Buccal b r (VII) 17. Parotid d u c t 18. Buccal n 13, plexus 19. Facial v. G masseter m. 20.Buccal p o u c h 21. Marginal mandibular br: (VII) 2 2 E x t e r n a I nasal bc 23.Mental nn. Fig. 4 Lateral view of the cutaneous branches of the trigeminal nerve with segments of the facial nerve. Part of the infratemporal fossa is also exposed. dorsal rami communicate with branches of the hypoglossal nerve as the latter nerve passes between the mylohyoid and hyoglossus muscles. Otic ganglion The ganglion is located on the medial side of the undivided portion of the mandibular division at the lateral aspect of the auditory tube. It is flat and measures approximately 3 X 6 mm. Several h e fascicles attach the ganglion to the division (fig. 3). The lesser petrosal nerve joins the ganglion dorsally. The ganglion sends a fine communication caudally to the auri- culotemporal nerve and also give origin to the very small tensor tympani nerve. Submandibular ganglion The ganglion is located between the hyoglossus and mylohyoid muscles in close association with the submandibular gland (figs. 2, 3). Two to three communications pass to the ganglion from the lingual nerve as the latter nerve travels medially in front of the medial pterygoid muscle. In addition to glandular branches, the ganglion also sends a branch to both the mylohyoid and medial pterygoid muscles and communicates with the mylohyoid nerve. BABOON TRIGEMINAL NERVE DISCUSSION The trigeminal nerve in the baboon has many similarities to that in man. However, the maxillary and mandibular divisions are unusually large which can be explained by the marked prognathism that this animal exhibits. O'phthalmic division The ophthalmic division is the smallest division. Christensen ('33) reported a simi1;u situation in the rhesus monkey. A collection of neuroblasts was observed by Gasser and Hendrickx ('69) in the medial part of the division during embryonic development which later became scattered and eventually disappeared. Later, during fetal development they observed in one 54 day old specimen a well defined ganglion on the medial side of the division. Attempts were made to locate grossly and microscopically such a ganglion in the adult but we were unsuccessful. The frontal nerve was found to be the largest branch of the division. Christensen ('33) reported the lacrimal to be the largest branch in the rhesus monkey. Lacroix ('27) mentioned that the frontal nerve is markedly developed in P. cynocephalus with a small medial and a larger lateral branch to the skin of the frontal region. Our dissections support his findings but in addition we found a smaller, more medial supratrochlear branch of the frontal nerve (figs. 1, 4, 5). No mention of supraorbital or supratrochlear branches of the frontal nerve in the rhesus monkey was made by Christensen ('33). Raven ('50) showed medial and lateral supraorbital branches and one supratrochlear branch in the 1. Zygomatic n. 2 Lacrimal n., zygomatic br: 3. Supraorbital nn. 4. Supratrochlear n. 5 lnfratrochlear n n. 6. Pa I p e bra I b r z 519 lnfraorbital nn. 8. Buccal plexus 9. lnfraorbital plexus 3 0. Facial n. 11. Marginal mandibular br: 12 Mental nn. Fig. 5 Frontal view of the cutaneous branches of the trigeminal nerve with segments of the facial nerve. 520 RAYMOND F. GASSER AND D. MILLER WISE gorilla. The stout communication that Gasser and Hendrickx ('69) observed between the frontal and trochlear nerves during embryonic development was not evident in the adult. We observed only that the nerves are adjacent for a considerable distance in the proximal part of their course (fig. 1). According to Lacroix ('27) the lacrimal nerve in P . cynocephalus divides into a medial branch that supplies the lacrimal gland, conjunctiva and eyelids and a larger lateral branch that leaves the orbit by a foramen in the region of the maxillo-malar (zygomatic) junction to become subcutaneous. We observed a similar pattern (fig. 1). Christensen ('33) indicated that in the rhesus monkey, the lacrimal nerve gives rise to a supraorbital nerve. This branching pattern could explain the larger lacrimal nerve reported in this animal. The course of the nasociliary nerve through the orbit and the branches of this nerve appear to be similar to that found by Christensen ('33) in the rhesus monkey. Several infratrochlear branches that innervate the skin on the root of the nose and an external nasal branch were found (figs. 4, 5). Raven ('50) illustrated one infratrochlear and two external nasal branches in the gorilla. Bowden, Mahran and Godding ('60) made no mention of a communication between the ophthalmic division and the facial nerve in baboons. We sometimes found a fine nerve fascicle connecting the zygomatic branch of the lacrimal nerve to the facial nerve in the infraorbital region (figs. 4, 5). Maxillary division According to Lacroix ('27) the maxillary division in P . cynocephalus gives rise to a small nerve that passes through the sphenomaxillary fissure and sends branches to the lacrimal gland. Gasser and Hendrickx ('69) reported that communications exist between the pterygopalatine and ciliary ganglia in baboon embryos. Our dissections revealed several orbital branches that course from the pterygopalatine ganglion to the orbital nerves as they pass through the superior orbital fissure (fig. 3). Such communications are probably the route whereby the lacrimal gland receives its secretomotor innervation. The zygomatic nerve from the maxillary division was found to have a variable course and branching pattern (figs. 2, 4, 5). The findings of Ashton and Oxnard ('58) support this. They observed no zygomaticotemporal nerve in the orangutan and in two of the four rhesus monkeys they examined. In one human dissection they reported that the zygomaticotemporal and zygomaticofacial branches arise separately. According to Raven ('50) each of these branches is present in the gorilla. The infraorbital nerve fascicles give off two superior alveolar nerves in the infraorbital canal which travel to the rostral maxillary teeth (fig. 3). The more lateral nerve has been referred to as the middle superior alveolar nerve. Fitzgerald ('56) reported that this nerve is present in four out of five human specimens he examined but Ashton and Oxnard ('58) saw only an anterior superior alveolar nerve and made no mention of a middle branch in Circopithecoidea (rhesus, baboon and guenon). The division terminates as five or six large infraorbital nerve fascicles which pass through separate foramina to innervate the skin of the lower eyelid, lateral snout and upper lip (figs. 4, 5). The foramina exhibit some variation in their size and location. Ashton and Oxnard ('58) pointed out the variability in the branching pattern of this nerve in Circopithecoidea. They described the nerve as leaving the skull through three infraorbital openings that are arranged in a characteristic pattern. However, in two of the baboons they studied, the nerve emerged through five separate foramina. Occasionally, we found six separate infraorbital nerves outside the skull. They made no mention of the palpebral branch we found in the baboon but they did observe twigs to the medial part of the lower eyelid in the orangutan, chimpanzee and man. In the gorilla, the nerve emerges from the skull through a solitary foramen (Raven, '50) as is also the case in man. Communications exist between the facial and the infraorbital and zygomatic nerves (figs. 4, 5). Gasser and Hendrickx ('67) demonstrated these communications in 45-54 day old baboon embryos. Numer- BABOON TRIGEMINAL NERVE ous communications were found between the maxillary division and the facial nerve in all of the primate types examined by Bclwden, Mahran and Godding ('60) which included the baboon. Mandibular division The nerve to the medial pterygoid arises from the undivided portion of the division or' from the adjacent otic ganglion (figs. 2: 3). In addition, fascicles from the nerve to' the mylohyoid course to the caudal portion of the medial pterygoid muscle. Schwartz and Huelke ('63) observed that in the rhesus monkey, the nerve to the medial pterygoid muscle arises from the posterior (dorsal) division. They also reported that the posterior portion is larger than the anterior (ventral) which is also tlhe case in the baboon. In addition, they found that the anterior division courses through the lateral pterygoid plate by passing through a pterygoalar foramen. Swindler ('67) and the present studies revealed the same arrangement in the baboon. The nerve to the mylohyoid is regularly ;Lbranch of the inferior alveolar nerve just before the latter nerve enters the mandible !:figs. 2, 3). Gasser and Hendrickx ('69) observed this arrangement during early liaboon development and Schwartz and :Huelke ('63) described a similar origin in the rhesus monkey. However, Christensen ('33) reported that in the rhesus, this nerve arises as a separate branch from the mandibular division just distal to the origin of the auriculotemporal nerve. Swindler ('67) indicated that the nerve can separate from the major trunk high up in the infratemporal fossa in the baboon. Four to five mental nerves were observed with variable size and position (figs. 2, 4, 5). Gasser and Hendrickx ('67) observed three to four mental nerve fascicles during development with each emerging from the mandible through separate foramina. Both Christensen ('33) and Schwartz and Huelke ('63) described only one mental nerve in the rhesus monkey and the illustration of Raven ('50) shows the same in the gorilla. We were able to isolate the submandibular ganglion which has communications with the lingual nerve as well as the 521 nerve to the mylohyoid and sends a branch to the mylohyoid and medial pterygoid muscles (figs. 2, 3). Christensen ('33) observed a submaxillary (submandibular) ganglion but Schwartz and Huelke ('63) were unable to fmd a discrete one in the rhesus monkey. Communications were found between the facial nerve (md the auriculotemporal, buccal and mental nerves (figs. 4, 5). This supports the finclings of Bowden, Mahran and Godding ('60). Gasser and Hendrickx ('67) observed these communications in 45-54 day old baboon embryos. The communications rewaled by the present study between the mental and facial nerves are not as numerous; or as prominent as those reported during development. Raven's ('50) drawing depicted similar communications between the mandibular division branches and the facial nerve in the gorilla. Numerous prominent communications exists between the lingual and hypoglossal nerves (fig. 3). In the rhesus monkey, Schwartz and Huelke ('63) observed one such communication. ACKNOWLEDGMENTS The authors wish to thank Dr. Andrew G. Hendrickx and the Southwest Foundation for Research and Education, San Antonio, Texas for supplying the embalmed specimens. Miss Cathy Chase and Mr. Charles Falk are acknowledged for their technical assistance. LITERATURE CITED Ashton, E. H., and C. E. Oxnard 1958 Some variations in the maxillary nerve of primates. Proc. Zool. SOC.London, 131: 457-470. Bowden, R. E.M . , Z. Y. Mahran and M. R. Godding 1960 Communications between the facial and trigeminal nerves in certain mammals. Proc. Zool. SOC.London, 135: 587-611. Christensen, K. 1933 The Anatomy of the Rhesus Monkey. Chap. XV. G . C. Hartman and W. L. Straus, Jr., eds. Williams and Wilkins Co., Baltimore, pp. 290-306. Fitzgerald, M. J. T. 1956 The occurrence of the middle superior alveolar nerve in man. 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