second or normal part of the mylonyoideus. The fourth portion at its anterior part arises from the angle of the jaw, then from the base of the cranium, and afterward from a strong fascia extended thence backward, between the post-cranial prolongations of the nose and mouth; the posterior and longest fasciculi come off more outwardly, and radiate to spread over and blend with the gular fasciculi of the sternoglossi, passing outward and downward, and then bending inward to envelope that part of the hyoid apparatus. All the fibres of the fourth portion terminate in a median raphé, which is less marked than in the anterior portion. The fibres of the posterior division of the mylohyoideus, especially those which are attached to the under surface of the posteriorly prolonged nasal canal, form a kind of muscular sheath for the basal part of the muscles of the tongue.

The cerato-hyoideus arises from the cerato-hyal: its fibres converge and form a fasciculus which is inserted into the commissural tendon of the genio-hyoid, and is connected with a strip from the sternomaxillaris. After giving attachment to the foregoing two muscles, and to the anterior constrictor of the pharynx, its extremity is attached to the stylo-hyoideus muscle.

In most mammals the hyoid arch, by the length of the ossified part of the stylohyal and the extent of the ossification of the ceratohyal is almost restricted to hinge-movements forward and backward upon the proximal joints of the stylohyals as a fixed point; so that the basihyal with the tongue cannot be very far protruded or retracted. In the Myrmecophaga jubata the usual place of the stylohyal is occupied by a long and slender muscle, the stylohyoideus, which arises from the petromastoid, and after a course of five inches is inserted into the ceratohyal, here the first bone of the hyoid arch. Supposing the stylohyoideus to contract one-third of its length, it would protract the hyoid arch to the same extent in which act it combines with the geniohyoideus. The retraction of the hyoid arch is provided for by the sternothyroidic and their continuations, the thyrohyoidei.

The geniohyoideus arises by a single tendon from the symphysis of the jaw, runs back beneath the raphé of the anterior mylohyoideus, slightly expands beneath the raphé of the middle mylohyoideus, then again contracts and again expands, and at about ten inches from its origin becomes diffused into fleshy fibres, which gradually acquire a breadth of six lines, continue back in close connection with the mylohyoideus to the commissural tendon, and there expand, the lateral borders being attached

of which the base of the tongue is situated, and here they converge and blend with corresponding flattened fasciculi, sent off from the lower part of the genioglossi, as these pass backward to the base of the tongue. The main continuation of the sternoglossus, i, forms a rounded slender muscle, which raises the buccal membrane so as to form the back part of the frænum linguæ, penetrates the back part of the base of the tongue, and constitutes a great proportion of its substance.

The genioglossus, ib. m, n, o, has a complex origin, by a middle portion, from the short symphysis mandibulæ, and by a flattened penniform series of fibres, form the lower border of the mandibular rami for the extent of four inches behind the symphysis. The symphysial origin is round and slender, and belongs more directly to the proper tongue-muscle: the ramal origins seem to be the more special fixed point of the subgular fasciculi. The fibres of the latter origin pass obliquely backward and inward, converging to a middle raphé, to which the symphysial origin closely adheres. The two origins of the muscle are blended into one for about three inches beyond the point of attachment, in which extent the muscle forms a moderately thick depressed mass along the middle of the under part of the mouth. It then begins to expand, and to detach from its under surface those subgular fasciculi, which diverge and unite with the corresponding dismemberments of the sternoglossi. The main part of the genioglossus enters, as a single muscle, the fore part of the base of the tongue, carrying into the floor of the mouth a fold of buccal membrane forming the fore part of the frænum linguæ.

Beneath the insertions of the geniohyoidei, a pair of more slender muscles, epihyoglossi, come off from the median ends of the epihyals. These muscles, after a brief course, expand into a thin layer, resolve themselves into separate fasciculi, and combine an inch in advance of their origin to form a layer about eight lines in breadth below the middle line of the post-lingual part of the mouth, which layer slightly diminishes in size as it approaches the commissure of the sternoglossi, and, with them, penetrates the back part of the frænum linguæ.

§ 196. Muscles of Cetacea.-In the Cetacea the muscles of the trunk are chiefly developed: those of the limbs are restricted to the pectoral pair. Swimming is the principal mode of progression in the muticate orders of Gyrencephala: but the phytophagous Sirenia have the power, in order to feed upon marine or littoral plants, of crawling at the bottom of the sea and shuffling along

the shore by means or aid of their anterior members, which in the true Cetacea are exclusively natatory organs.

The head, in these, has so little mobility, that its axis can be but slightly altered, without that of the body altering also. With bones so short, so little mobile, and extensively co-adapted or anchylosed, as the vertebræ of the neck, muscles proportionately reduced should correspond. The cervical muscles are, nevertheless, much the same in number as in other Mammals; but their shortness and thinness, principally in those attached to the atlas and the axis, are extreme. The homologue of the splenius capitis,' fig. 10, h, is the best developed: it comes off from the anterior dorsal and cervical series of neural spines, and its fibres converge to be inserted into the paroccipital ridge.

The muscles of the back present no other important modifications than their great developement, especially where they are prolonged upon the caudal vertebræ. Thus the longissimus dorsi and the sacro-lumbalis are attached anteriorly to the skull, and posteriorly transmit their tendons, the first to the end of the tail, the second to all the transverse processes of this part of the spine, associating its movements, especially in the vertical direction, with those of the back. The levator caudæ takes its rise above the five or six dorsal vertebræ, under the longissimus dorsi, and often in this part blends with it; it then extends freely as far as the extremity of the tail, where the two muscles unite together again by their tendons. They are opposed by a depressor caudæ, of great thickness, which proceeds from the thoracic region, attached by tendinous slips to the ribs and the contiguous transverse processes; it is inserted into the hæmal arches of the tail. A muscle passes from the rudimental bones of the pelvis to the hæmapophyses of the anterior portion of the tail. The great recti abdominis and obliqui ascendentes muscles are continued backward from the abdomen, and attach themselves behind to the sides of the anterior caudal vertebræ. By this aggregation of muscles the tail of the Cetacea expands to proportions of the trunk, and acquires the prodigious strength which it possesses for propelling the most gigantic of the species, with ease and swiftness, through the water; and, by means of the horizontal expansion of the caudal fin, it enables them to readily ascend to the surface to respire and again seek protection in the deep abysses of the ocean.

In the great pectoral muscle, part of which is shown in fig. 10, at g, the costal origin is extensive, and the portion which comes off from the short sternum, passing transversely each to its own

humerus, closely resembles the transverse connecting fasciculus in the Mole.

The muscle answering to 'levator scapula,' b, rises from the paroccipital, as well as from the cervical diapophyses: it expands to be inserted into the fore and upper angle of the scapula

and the fascia covering the 'infraspinatus:' it is a protractor, or forward rotator, of the scapula. The rhomboideus,' a, is the raiser of the blade-bone. Two strong muscles attached to the paroccipital and mastoid, pass, one, e, to the sternum (sternomastoideus), the other to the humeral tuberosity (sterno-humeralis). The latissimus dorsi,'f, is short and slender, coming off by a few digitations from the ribs, and inserted into the humerus and by an extended aponeurosis into the olecranon. The 'supraspinatus' is small: it is covered by the deltoid,' i. The infraspinatus,' c, is a broad and thin sheet of muscle. Behind it is a 'teres major,' k, also of broad and flat form; and a thick and narrow teres minor,' l. The serratus magnus' does not extend forward beyond the ribs of the dorsal vertebræ.

6

In the Ungulate series the muscular system has been traced out in both Perisso- and Artio-dactyle species, but most completely in the Horse, figs. 11-13. In this sensitive quadruped the dermal muscles are well developed, enabling it to shake tl