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In some Marsupials the optic nerve grooves the orbito-sphenoid, escaping by a cleft continuous with the fissura lacera anterior1: in higher Mammals the nerve escapes by a special foramen opticum.' The extra-cranial parts of the nerves are remarkably long in Whales, and in all Cetacea they diverge from the chiasma

2

at a wide angle, fig. 60, 2, 2.

Mammals rise to Man, fig. 128, b.

The oculo-motor or third' nerve, fig. 60, 3; fig. 128, c, and

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the fourth,' fig. 128, d, have the same origin, distribution, and connections with the sympathetic, as in Man. The branch of the 'third' nerve, which runs along the lower part of the eye-ball, between the inferior' and external' rectus muscles, and supplies the obliquus inferior,' is connected, usually by a short thick cord, with a lenticular ganglion;' but this is not so well defined in some Mammals, and the ciliary nerves are usually fewer than in Man. The fourth nerve supplies the obliquus superior' muscle. In the Sheep this nerve receives some branches from the ophthalmic division of the fifth' nerve. Besides the 'rectus externus,' the sixth nerve, fig. 128, f, in most Mammals, supplies an additional muscle, the retractor oculi.' The fifth' or 'trigeminal' nerve, fig. 128, e, e', is commonly the largest of the cerebral nerves, and resembles the myelonal nerves, fig. 136, in having a ganglionic, fig. 230, 9, 10, and a non-ganglionic, ib. 11, portion, the latter being motory,' supplying muscles, the former distributed to sensitive and secerning surfaces. This distinction is better marked in Mammals than in Birds and Reptiles : like which, however, the ganglion is single, not divided, as in most Fishes (vol. i. figs. 201, 202). The size of the 'fifth' nerve relates to the perfection or sensitiveness and application of those surfaces, not to the proportion of the facial to the cranial part of the head. Thus we find the fifth or trigeminal nerve of largest relative size in the Ornithorhynchus paradoxus, which uses, like the duck, its beak as a tactile instrument in the detection of its food. Emerging from the ganglion, fig. 51, o', anterior to the pons, ib. c, it soon divides into three branches, the first and second appearing as one. The first and smallest division divides into two equal branches: the superior or ethmoidal branch enters the nose, combines, in part, with the olfactory, for the service of the pituitary membrane; but mainly emerges from the nasal cavity, supplies the skin at the upper part of the face, and, by a branch continued from between the nasal and premaxillary bones, is distributed to the nostrils and contiguous integument. The second division of the fifth is two lines broad and one line and a half thick: after emerging by the foramen rotundum, the chief part of it passes through the ant-orbital canal, and divides into two branches, distributed, the one to the nasal or upper parietes of the face, the other to the lateral or labial integuments. The palatine branch divides into a posterior smaller nerve, which passes through the posterior palatine foramen: the anterior and larger branch emerges from the anterior palatine canal, and supplies Jacobson's organ at the floor of the nose and the palatine membrane.

The third division of the fifth is broader but thinner than the second; it leaves the cranium by the foramen ovale, and is distributed as usual, mainly to the sensitive labial integument of the lower jaw, fig. 3, a, a: its non-ganglionic part goes to the manducatory muscles.

In the Echidna the trigeminal is of smaller size, and its first and second divisions are much less in proportion to the third, which supplies, from its ganglionic part, the sensitive and secreting surface of the long tongue. This size of the lingual branch of the trigeminal is still more marked in the Pangolins and Anteaters, especially in Myrmecophaga jubata. A distinct gustatory nerve, communicating with a motory facial' nerve by a' chorda tympani,' is a mammalian characteristic of the trigeminal. In the Hedgehog the nasal branch is the largest of the first division: after dismissing a few ciliary nerves it quits the orbit and enters its special canal at the fore part of the large cribriform plate, and divides on entering the nasal cavity into the external and septal branches, the latter being the largest, and richly spread upon the pituitary membrane of the septum and inferior turbinal. The

bulbs of the vibrissæ in the Hedgehog and other Insectivora use a large proportion of the facial branches of the maxillary and mandibular divisions of the fifth. In Rodents the dental branches of these divisions are large, and especially the nerves sent therefrom to the active and persistent pulps of the scalpriform incisors; and they show, especially in the mandible, a recurrent course, as I found in the dissection of the Porcupine, fig. 129, "i.' The nasal and labial nerves are large in Moles and Shrews, especially the long-snouted kind (Rhynchocyon). But the chief peculiarity of

xx. vol. i. p. 103, prep. no. 357B.

the trigeminal in Talpida is the share which the ophthalmic division of the fifth' takes in the function of the reduced eye-ball, as

a

130

Trigeminal nerve of Mole.
LXIII".

a warner of light. In fig. 130, a is the trigeminal, the ganglionic part, c the third or mandibular division, f the second or maxillary division, d the first or ophthalmic division, of which the branch going to the eye, e, is large, while that going to the nose, g, is small, reversing the proportions in the Hedgehog. In many Lissencephala the part to which the root of the trigeminal can be traced makes a small prominence on each side the fore end of the calamus scriptorius.' In the Elephant the superorbital and superficial nasal branches of the first' division, but more especially the 'facial' branch of the second' division, which emerges from the antorbital foramen, present a large size in relation to the proboscis. The size of that foramen is not, however, always indicative of that of the nerve. In many Rodentia a part of the masseter traverses, with the antorbital nerve, the foramen in. question, which is, then, enormous, as in figs. 234, 238, 241, v (vol. ii. p. 377). The dentary branch of the maxillary exceeds that of the mandibular division of the fifth in the Elephant, to meet the demands of the persistent matrix of the tusk. But this difference in the size of the nerves supplying the upper and lower jaws is maximised in the Balanidæ, in relation to the active and extensive growth of baleen in the upper jaw, and the absence of teeth or their substitutes in the lower jaw. The palatine nerves supplying the baleen-pulps are as thick as the finger in Balena mysticetus. In the Porpoise (Phocana) an orbital branch joins a plexus near the fore part of the orifice of the eye-lids, sent off from the seventh' or facial nerve, from which union branches pass to the muscles and membrane of the blow-hole. The maxillary branch sends off a subcutaneus mala,' which combines with the facial nerves to supply the inferior palpebral muscle, and spread upon the hind part of the palpebral opening. There are five or six antorbital branches which run forward between the maxillary periosteum and the superincumbent muscular and tegumentary layer, emerging to spread upon the latter where it forms the upper lip or margin of the mouth, and also sending a recurrent branch to the blow-hole. A large branch of the maxillary passes

through the foramen near the upper opening of the nasal passage, and ramifies upon the plicated membranes of the blow-hole. The dental nerves are large from both maxillary and mandibular divisions of the fifth: the gustatory branch is, relatively, small; and sends off a filamentary chorda tympani,' which may be traced to the trunk of the facial, and is connected, in its course, with the carotid plexus of the sympathetic.

In Ruminantia the first division of the fifth' subdivides into frontal and nasal: the latter supplies the upper part of the septum and the superior turbinal, and sends a few branches to the fore part of the nose, which meet these filaments reflected from the second division of the fifth. The branches to the lacrymal and harderian glands, to the eyelids, and the larger one which passes out of the orbit to the integuments of the temple, and which chiefly supplies the horn-core, or the growing antler, may be traced back distinctly to the Gasserian ganglion. The second division of the fifth, escaping by the foramen rotundum, sends antorbital branches to supply the upper lip, the nostril, and the pituitary membrane at the lower part of the nose. It also sends off the lateral nasal, receiving the vidian' nerve, and supplying the inferior turbinal: lastly, the palatine and upper dental nerves. The ganglionic part of the third division gives off the buccal nerve,' connected with an 'otic ganglion,' supplying the superficial muscles and skin behind the angle of the mouth, and communicating with branches of the 'seventh' or facial nerve; the large branch dividing into the inferior dental and gustatory nerves, the latter receiving the 'chorda tympani:' lastly, the external auricular, passing behind the mandibular ramus, joining the middle branch of the seventh,' and supplying the muscles of the ear, but mainly distributed to its sensitive surface.1 The non-ganglionic part of the fifth supplies the temporal, masseter, and pterygoid muscles, also the mylohyoid and anterior part of the occipito-hyoid or digastric: the part going to the otic ganglion is continued therefrom to the internal pterygoid and to the muscles of the soft palate. A ganglion called 'submaxillary' and situated near the deeper part of the gland so named, is connected by filaments with the gustatory nerve.

In Swan's dissection of the cerebral nerves of the jaguar he found the superior nasal sending a branch to join the one from the lenticular ganglion to form ciliary nerves, and then pass forward to send one branch into the nose and another to the skin See dissection of the trigeminal of Bos, in LIV, pl. xxxii. fig. 3.