6 ANATOMY OF VERTEBRATES. 



cartilage of the first rib, the manubrium sterni, and the coracoid 

 bone. 



The diaphragm presents the structure which is characteristic 

 of the true mammiferous animal. The lesser muscle arises from 

 the first lumbar and four last dorsal vertebrae, and expands to be 

 inserted into the central tendon, which chiefly receives the fibres 

 of the greater muscle arising from the cartilages of the eleven 

 inferior pairs of ribs. 



The pectoralis, 2, is of very striking dimensions ; the origin of 

 the superficial portion extends from the acromion and episternum, 

 along the sternum and linea alba, almost to the pubis ; a deeper- 

 seated portion arises from the six osseous sternal ribs ; the fibres of 

 both portions converge to be inserted into the largely-developed 

 pectoral or anterior crest of the proximal half of the humerus. 



The pectoralis minor is attached to the coracoid, and the sub- 

 clavius is likewise inserted, as in some other quadrupeds, into 

 this bone, which is no longer a subordinate process of the scapula 

 in the Monotremes. 



The subscapularis is a narrow muscle, and narrower in reality 

 than at first sight it appears to be, since the supraspinatus, from 

 the inflection of the spine and acromion, arises from the same 

 aspect of the scapula, and appears to form the anterior fasciculus 

 of the subscapularis; its distinct insertion into the anterior 

 tubercle of the head of the humerus points out its true nature. 



The infraspinatus, 20, and the large teres major cover the 

 whole external surface of the scapula. 



The deltoid is divided into an anterior and a posterior portion. 

 The anterior portion, 19, arises from the anterior extremity of the 

 coracoid, and is inserted into the summit of the deltoid crest of 

 the humerus: the posterior part, 21, arises from the anterior and 

 superior apex of the scapula, and is inserted into the lower half of 

 the deltoid crest. There are also two muscles to which the name 

 coraco-brachialis may be applied, a superior one, 22, and an in- 

 ferior one, 25. 



The biceps brachii arises by two heads ; one, 23, arises from the 

 sternal extremity of the coracoid, the other, 24, also arises from 

 the coracoid ; the common tendon is inserted into the middle of 

 the radius. 



The other muscles of the anterior extremity adhere closely to 

 the Mammalian type. The extensor carpi radialis, 30, sends three 

 tendons, to be inserted respectively into the second, third, and 

 fourth metacarpal bones. There is a single common flexor digi- 

 torum, as well as extensor digitorum, 2:. 



The extensor digiti minimi, 26, the indicator, 28, the extensor 



