Of the One-Humped Camel

Home , Buccinator muscle, Temporal muscle

J. Anat. (1970), 106, 2, pp. 341-348 341 With 3 figures Printed in Great Britain The course and branches of the facial nerve of the one-humped camel

I. ARNAUTOVIC, M. E. ABU SINEINA AND M. STANIC Faculty of Veterinary Science, University of Khartoum (Received 14 February 1969) The course and ramification of the facial nerve of the camel have not previously been clearly established, and the brief references that occur in the literature are of a rather general kind. Thus Lesbre (1906) stated that the cranial nerves of the camel were similar to those of ruminants, and Leese (1927) concluded that there were no significant differences between the course of the facial nerve of the camel and that of other ruminants. Droandi (1936) gave a more detailed account of the facial nerve which he described as ramifying on the external surface of the head. Tayeb (1958), who studied the cranial nerves of the camel, did not give the full account of the facial nerve. MATERIAL AND METHODS During the period July 1966 to December 1967 the heads of fifteen camels slaugh- tered at Tamboul Slaughterhouse, south-east of Khartoum, were collected for dis- section at the Faculty of Veterinary Science, Shambat. The heads belonged to normal healthy animals, seven males and eight females, varying in age from 4 to 10 years. Both sides of each head were used in the study. The heads were removed, with their skin intact, from the carcasses at the level of the third cervical vertebra. Some of the specimens were dissected immediately after collection, others were injected with 10 % formalin and studied later.

OBSERVATIONS The facial nerve, which originates from the lateral part of the trapezoid body immediately behind the pons, enters the facial canal through the porus acusticus internus. After it emerges through the stylomastoid foramen it assumes a ventral and somewhat oral direction for about 2 cm (Fig. 2 [1]), after which it divides into two main branches; a large dorsal branch (n. buccalis dorsalis, Fig. 2 [2]) and a smaller ventral branch (n. buccalis ventralis, Fig. 2 [3]). After it emerges through the stylomastoid foramen the facial nerve gives off four branches before if bifurcates. These are as follows: (1) At the level of the stylomastoid foramen the facial nerve gives off a very small branch, the posterior auricular nerve (Fig. 2 [4]). This originates from its caudal border and for 2-3 cm assumes a caudo-dorsal direction, 3-5 mm posterior to and parallel with the caudal margin of the auricle. Then it ramifies posteriorly and dorsally in the muscles and skin of the ear. This branch sometimes separates from the facial nerve before it emerges through the stylomastoid foramen. 342 I. ARNAUTOVIC, M. E. ABU SINEINA AND M. STANI_6 (2) From the dorsal border and approximately 1 cm after emerging through the stylomastoid foramen, it gives off an internal auricular nerve which, after a short while, enters the interior ofthe auricle where it ramifies (Fig. 2 [5]). Before reaching the interior of the auricle the internal auricular nerve often gives off a very small branch which supplies the oro-dorsal part of the parotid gland. Occasionally the internal auricular nerve leaves the facial nerve before the latter emerges from the stylomastoid foramen. In three cases both the internal auricular and the posterior auricular nerves left the facial nerve through a common trunk.

Fig. 1. Muscles and superficial nerves of head of camel (lateral view). a, masseter; b, buccinator; c, zygomaticus; d, depressor palpebralis inferioris; e, lacrimalis; f, levator communis naso- labialis superioris; g, risorius. 1, ventral branch of facial nerve; 2 & 3, dorsal branch of facial nerve; the auriculo-palpebral nerve lies immediately in front of the auricle. (3) From its ventral border about 1 5 cm after it leaves the stylomastoid foramen, the facial nerve gives a branch which runs ventrally to, and ramifies in, the deep layers of the middle part of the parotid gland (Fig. 2 [6]). (4) From its ventral margin, the facial nerve gives off a small branch, which more or less corresponds to the digastric branch in the horse, about 17 cm after emerging through the stylomastoid foramen (Fig. 2 [7]). The branch runs in a caudo-ventral direction under the dorsal part of the parotid gland; it then pierces the parotid gland about a third of the distance from its lower border and lies on its surface. Here it is covered by the caudal part of the risorius muscle. * It continues in the same direction for about 2-3 cm after which it ramifies in the risorius muscle. * Terminology after Tayeb (1951) and Droandi (1936). r, ' 1 nerve of camel 343 The facial nerve divides into two main branches about 2 cm ventral to the lower margin of the external acoustic process. The smaller of these, the ventral buccal nerve, runs ventrally and passes under the parotid gland. The nerve then pierces the medial surface of the parotid gland at its centre and continues in the same direction within the parenchymatous tissue. Finally, it leaves the gland at the level of the angle of the mandible close to the caudal margin of the vertical part of the ramus. From this point, the nerve takes an oro-ventral direction, passes over the lateral surface of the masseter muscle and is covered by the caudal part of the risorius muscle and the

Fig. 2. Nerves and muscles of head of camel (lateral view). 1, Facial nerve; 2, dorsal branch of facial nerve; 3, ventral branch of facial nerve; 4, posterior auricular nerve; 5, internal auricular nerve; 6, branch to parotid gland; 7, branch of risorius muscle, 8, branches to parotid gland; 9, communicating branches of the superficial temporal and dorsal buccal nerves; 10, auriculo- palpebral nerve; lOa, auricular branch; lOb, temporal branch; 10c, zygomatic branch; 11, branch to risorius muscle; 12, branches to risorius, buccinator and zygomatic muscles; 13, communicating branch from buccinator nerve; 14, branch to the angle of the mouth; 15, infraorbital nerve. skin. It continues in an oro-ventral direction parallel to, and at a distance of 3-4 cm above, the ventral margin of the horizontal part of the ramus. It is covered by the risorius muscle until the level of the oral margin of the masseter muscle is reached. Thereafter, it runs in the same direction along the ventral border of the buccinator and underneath the risorius, parallel to and at a distance of 2-3 cm above the ventral margin of the horizontal part of the ramus. Just in front of the mental foramen (Fig. 3 [3 a]), it joins the mental branch of the mandibular alveolar nerve and forms an extensive plexus which sends branches to the lower lip and the chin. 344 I. ARNAUTOVIC, M. E. ABU SINEINA AND M. STANIt From the point at which the ventral buccal nerve separates from the main trunk until its communication with the mental branches it gives off the following branches: (1) While passing underneath and within the parotid gland it supplies the latter with three to five small branches which leave the nerve at variable distances (Fig. 2 [8]). (2) It gives off small branches to the occipito-mandibularis, risorius and buccinator muscles, as well as to the buccal glands. (3) It receives two communicating branches, a larger one about 5-6 cm in front of the angle of the mandible (Fig. 2 [9]) and a smaller one just behind the oral border of the masseter muscle (Fig. 2 [9]). These branches originate from a communication between the~~~~~~~~~~~~~~~~~~~~~~~ventral branch of the superficial 3temporal and dorsal buccal nerves.

Fig. 3. Diagram showing the nerves of head of camel. 1, Facial nerve; 2, dorsal branch of facial nerve; 3, ventral branch of facial nerve; 3a, mental branch; 4, posterior auricular nerve; 5, internal auricular nerve; 6, branch to parotid gland; 7, branch to risorius muscle; 8, branches to parotid gland; 9, communicating branches of the superficial temporal and dorsal buccal nerves; 9 a, communicating branch of the alveolar mandibular nerve; 10, auriculo-palpebral nerve; 10a, auricular branch; 0b, temporal branch; 10c, zygomatic branch; 11, branch to risorius muscle; 12, branches to risorius, buccinator and zygomaticus muscles; 13, communicating branch from buccinator nerve; 14, branch to the angle of the mouth; 15, infraorbital nerve.

(4) About 5-6 cm from the midpoint between the angle of the mandible and the mental foramen, the ventral buccal nerve joins a nerve which is about 2-3 times larger than itself. This nerve emerges from a large foramen situated about 2-3 cm in front of the mid-point between the angle of the mandible and the mental foramen (Fig. 3 [2]). This foramen exists only in the camel. Droandi (1936) called it the anterior opening of the canalis dentalis inferioris. The nerve which emerges from this foramen was traced inside the horizontal part of the ramus and found to be a branch of the Facial nerve of camel 345 mandibular alveolar nerve. When it emerges through the foramen, it takes an oro- ventral direction 2-2 5 cm above and runs parallel to the ventral border of the horizontal part of the ramus until it joins the ventral buccal nerve. After joining this nerve, the ventral buccal nerve becomes more than twice the size of the trunk of the facial nerve after it emerges through the stylomastoid foramen. In its further course the ventral buccal nerve proceeds oro-ventrally and is partially covered by the ventral part of the buccinator muscle (Fig. 1 [1]). It gives off a number of branches to the buccinator muscle as well as communicating filaments to the buccinator nerve. The dorsal buccal nerve, the larger of the two branches, runs in an oro-ventral direction along the medial surface of the oro-dorsal part of the parotid gland. Then it bends even more orally, emerges from beneath the parotid gland and runs over the lateral surface of the masseter muscle about 4 cm below the ventral border of the zygomatic arch. It is covered by the aponeurotic ventral origin of the zygomaticus muscle and by the superficial fascia (Fig. 1 [2]). The nerve then continues along the medial surface of depressor palpebralis inferioris muscle which, to a great extent, is covered by the zygomaticus muscle. Crossing the anterior border of depressor palpebralis inferioris muscle it lies for a short distance under the zygomaticus muscle. At the level of the medial angle of the eye it runs for about 1-1 5 cm on the lateral surface of the buccinator muscle where it is covered only by the fascia and the skin (Fig. 1 [3]). It continues in this oral direction piercing the lateral surface of the ventral part of the lacrimalis muscle (malaris muscle) to run within it and reach the medial surface of the latter near to where this joins levator communis naso-labialis superioris muscle. The nerve then lies for a short distance under the ventral part of the medial surface of levator communis naso-labialis superioris. It continues under a muscle which corresponds to the levator labii superioris proprius, dilator naris lateralis and depressor labii superioris muscles of the ox and ends in the upper lip. From the point at which the dorsal buccal nerve separates from the main trunk until it ends in the upper lip, it gives off the following branches: (1) From the dorsal and ventral margin of that part of the nerve that lies immediately under the parotid gland it gives off two to three branches that end in the dorsal part of the gland. (2) At about 1 cm after the bifurcation of the main trunk, the dorsal buccal nerve gives off a very large nerve from its dorsal border. This is the auriculo-palpebral nerve (Fig. 2 [10]), which is larger in size than the ventral buccal nerve but smaller than the dorsal buccal nerve. The auriculo-palpebral nerve pursues an oro-dorsal course, at first covered by the oro-dorsal part of the parotid gland. It continues on this course 1-1 5 cm oral to the cranial part of the base of the auricle and passes over the aboral part of the zygomatic arch where it divides into three branches: (a) A smaller auricular branch which continues in the same direction as the main trunk, and after a course of 1 5-2 cm gives off numerous small branches that innervate the anterior auricular muscles and the skin over the oro-dorsal part of the auricle (Fig. 2 [10a]). Communicating filaments unite with the dorsal branches of the temporal superficial nerve. (b) A temporal branch, which takes an oro-dorsal direction and then passes across the whole surface of the temporal muscle to which it gives few filaments. It then ends by dividing into several branches that innervate the scutularis, temporalis, 346 I. ARNAUTOVIC, M. E. ABU SINEINA AND M. STANIC orbicularis occuli and the beginning of lacrimalis muscle (Fig. 2 [lOb]). It also sends communicating filaments to branches of the ophthalmic nerve. (c) A zygomatic branch which runs in an oral direction for about 0 5-1 cm dorsal and parallel to the zygomatic arch and ends by dividing into 3-5 branches that innervate the external muscle of the eye, the palpebra and the skin (Fig. 2 [lOc]). This branch, the zygomatic itself, gives off a branch which communicates with branches from the frontal and lacrimal nerves thereby constituting a plexus. Immediately after its detachment from the dorsal buccal nerve and before it divides into three branches, the auriculo-palpebral nerve gives off several small branches to the oro-dorsal part of the parotid gland. It also receives several branches from the ventral branch of the superficial temporal nerve. (3) At about 05 cm oral to the origin of the ventral buccal nerve, the dorsal buccal nerve gives off a small branch that runs in an oro-ventral direction under cover of the dorsal part of the parotid gland (Fig. 2 [11]). It then pierces the parenchymatous tissues of the gland, running in the same direction until, about the middle of the gland, it gains the lateral surface of the latter. Here it lies immediately under the risorius muscle. At level of the angle of the mandible it ramifies in the middle part of the risorius muscle. During its course, this branch gives filaments to the parotid gland. It is worth mentioning that immediately after its origin this nerve runs in front of the ventral buccal nerve, to which it is attached by loose connective tissue, to the level of the angle of the mandible. That is why it is rather difficult to distinguish this nerve. (4) About 1 cm in front of the auriculo-palpebral nerve it gives off from its dorsal border a small branch that communicates with the ventral branch of the superficial temporal nerve. This communicating branch supplies the parotid lymph gland and the dorsal part of the masseter muscle. (5) It receives one communicating branch which originates from the ventral branch of the superficial temporal nerve, just before the dorsal buccal nerve emerges from underneath the parotid gland. (6) Just in front of the point where the dorsal buccal nerve emerges from underneath the parotid gland, it gives off from its ventral border some fibres which join the remainder of the fibres from the ventral branch of the superficial temporal nerve (Fig. 2 [12]). This branch runs oro-ventrally to supply the risorius, buccinator and the zygomaticus muscles and finally communicates with the ventral buccal nerve. (7) Immediately cranial to the oral margin of the masseter muscle, the dorsal buccal nerve receives 2-3 large communicating branches that originate from the buccinator nerve (Fig. 2 [13]). One of these branches partially communicates with the dorsal buccal nerve and the rest of its fibres, together with some of the fibres of the dorsal buccal nerve, passes for about 1-2 cm over the latter and ramifies at the angle of the mouth (Fig. 2 [14]). Before it ends, this branch gives off a filament that supplies the buccinator and the zygomaticus muscles. (8) An exceptionally large nerve, the infraorbital, which is larger than the facial trunk, communicates with the dorsal buccal nerve at the level of the middle of the interalveolar space (Fig. 2 [15]). The reinforced dorsal buccal nerve proceeds along its previous course ending in the muscles and skin of the upper lip. Facial nerve of camel 347

DISCUSSION Although there is some similarity between the course of the facial nerve of the camel with that of the horse and ox, a number of differences are found. These are typical of the camel. The works of Lesbre (1916), Leese (1927) and Droandi (1936) do not give information for discussion. There are, however, significant differences between our findings and those of Tayeb (1958). Tayeb stated that at its origin, the facial nerve in the camel is covered by the cutaneus faciei muscle. We could not however find this muscle in any of the specimens dissected. Instead, the nerve was found to be covered at first by the aponeurotic beginning of the zygomaticus muscle. It runs medial to the zygomaticus and depressor palpebrae inferioris muscles and then passes along the dorsalborder ofthe zygomaticus muscle where it lies immediately under the skin for about 2-3 cm before it passes under the malaris (lacrimalis) and levator communis naso-labialis superioris muscles. The nerve described by Tayeb as proceeding cranially from the border of the parotid gland and then becoming cutaneous on the posterior surface of the risorius muscle was not found, and we believe that the nerve described by him is in fact the ventral branch of the temporal superficial nerve which, after its detachment, proceeds oro-ventrally and partially communicates with the dorsal buccal nerve, the rest of its fibres together with more fibres from the dorsal buccal nerve continuing oro-ventrally on the lateral surface of the masseter muscle to supply the masseter, risorius, depressor palpebrae inferioris and the buccinator muscles. It is not possible to compare the present findings regarding the ventral buccal nerve with those of Tayeb as that author did not clarify the orientation of this nerve; neither did he pay attention to the numerous communications of the facial nerve which we believe to be of great significance as far as the function of this nerve is concerned. Our findings agree with those of Tayeb in that from the point at which it originates until it emerges from the stylomastoid foramen, the facial nerve of the camel does not differ from that of other domestic animals. The main differences between the facial nerve of the camel and that of the horse and ox are as follows: (1) The facial nerve of the camel gives off a branch which supplies the risorius muscle only. This nerve corresponds to ramus colli in the horse. (2) The posterior auricular nerve is smaller in the camel and does not communicate with thefirst and secondcervical nerves as in the horse(Sisson, 1966; Ellenberger, 1943). (3) The auricularis internus nerve gives off a branch which supplies the most dorsal part of the parotid gland. (4) A nerve which corresponds to the digastric nerve in the horse supplies the caudal part of the risorius muscle only. (5) The bifurcation of the facial nerve in the camel is nearer to the stylomastoid foramen than it is in the case of the horse and ox. (6) The ventral buccal nerve of the camel differs from that of the horse and ox in that it supplies the parotid gland with several branches, innervates the risorius muscle and receives a branch which is formed by fibres both from the superficial temporal and from the dorsal buccal nerves. It also forms an exceptionally large communicating branch with the mandibular alveolar nerve. 348 I. ARNAUTOVIC, M. E. ABU SINEINA AND M. STANIC (7) The dorsal buccal nerve gives off an auriculo-palpebral nerve which comprises the second large branch of the facial nerve. The auricular branch of the auriculo- palpebral nerve communicates with the dorsal branch of the superficial temporal nerve just in front of and dorsal to the auricle. The temporal branch gives off branches to the temporalis and the beginning of the lacrimalis muscles. The dorsal buccal nerve of the camel also differs from that of the horse and ox in that it gives off more branches to the parotid gland and innervates the dorsal part of the masseter and the depressor palpebrae inferioris muscles. It receives communications from both the ventral and middle branches of the temporal superficial nerve, the auriculo-palpebral nerve and two or three branches of the buccinator nerve. Before the end of its course, the dorsal buccal nerve forms a very large communication with the infra-orbital nerve. This is typical of, and peculiar to, the camel. It is of interest that the dorsal buccal nerve and its branches, together with the branches of the superficial temporal nerve, form a very extensive plexus in the region which is covered by the dorsal part of the parotid gland. The communications given in the text appeared in more than 75 % of the dissected specimens. The description of the facial nerve and its communications with other nerves should be of use in studies of its function and for the injection of local anaesthetics for veterinary purposes. SUMMARY The topography of the facial nerve of the camel has been studied in full. Its course and branching differ considerably from that in the horse and ox. Communications were observed with other cranial nerves which appear to be present only in the camel. The writers wish to record their gratitude to Mr Ahmed Abdel Mageed for the drawings and to Professor J. L. Cloudsley-Thompson for going through the script.

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