MYOLOGY OF REPTILES. 217 



attached anteriorly in part to the triangular short sternum, ex- 

 tending beyond it to the transverse part of the episternum, and 

 is thence continued (as in fig. 135, 27), to the symphysis mandi- 

 bulae, representing the geniohyoideus. A small fasciculus, fig. 141, 

 10, is also sent to the coraco-scapular joint. 



The upper jaw is fixed. The muscle which, by its insertion 

 into the lower jaw, acts as a temporalis, is divided into two 

 fasciculi ; one, fig. 140, 2, has the normal origin from the side of the 

 cranium; the other, ib. i, atlanto-mandibularis, acts with greater 

 force by deriving its origin from the neural arch and spine of the 

 atlas. The masseter, ib. 3, arises from the mastoid and epitym- 

 panic, and is inserted into the outer surface of the hinder half of 

 the mandible. The occipito-mandibularis, or digastricus, ib. 4, 

 arises from the paroccipital and back part of the epitympanic, 

 and is inserted into the angular element behind the tympano- 

 mandibular joint Avhereby it opens the mouth. In this action it 

 is aided by the strip, ib. 13, which passes from the angle of the 

 jaw upward to the skin. Some amount of lateral movement of 

 the mandible is effected by a pterygoid muscle. The retraction of 

 the mandible is provided by the muscle, ib. 13, although it seems 

 lost in the skin, as it passes backward from the angular process. 

 A mylohyoideus, fig. 141, 11, passes from one ramus to the other, 

 external to the geniohyoideus, ib. 8/, and to the following 

 muscles of the hyoid arch. The genio-ceratoideus, ib. u, arises 

 from near the symphysis mandibula?, and is inserted into the cera- 

 tohyal. The hyolranchialis, ib. is, passes from the base of the 

 ceratohyal to the hyobranchial cornu. 



With the growth and specialisation of the segments of the 

 limbs the muscles became larger, more numerous, and more dis- 

 tinct. The pectoralis, fig. 141, 16, 16, has its origin extended from 

 the fore part of the coracoid and episternum to the linea alba, or 

 aponeurotic continuation of the sternum, half an inch beyond the 

 coracoid ; the fibres converge to their insertion into the pectoral 

 ridge of the humerus ; but so that the coracoid portion is almost 

 a distinct muscle. This muscle suspends the fore part of the 

 trunk upon the fore-legs, and besides depressing the humerus, 

 rotates it in the plane of the body's axis as different portions of 

 the muscle come into action. 



A muscle, fig. 140, n, arising from scattered fibres by a longi- 

 tudinal tract of the aponeurosis, covering the loncjissimus and 

 spinalis dorsi, collects those fibres and contracts as it descends 

 over the hind part of the scapula to be inserted into the back part 

 of the pectoral ridge. An anterior part, ib. 22, of the same 



