4 GUIDES FOR VERTEBRATE DISSECTION 



Turn to the lower surface, lift up the posterior margin of the 

 external ceratohyoid and expose (9) the internal ceratohyoid 

 muscle, extending outwards and backwards from the hyoid 

 cartilage to its insertion on the cartilage of the first branchial arch. 

 Near the insertion of the internal ceratohyoid is (10) the 

 constrictor arcuum, which extends across the branchial arches 

 from the first to the third. 



Farther out (i.e., more lateral) upon the branchial arches will 

 be found fibres of (11) a depressor arcuum branchialium, the 

 origin of which is best seen later, after the removal of the 

 cucularis and omohyoid muscles. 



Muscles of the Shoulder-girdle. Just behind the mylohyoid 

 muscle on the latero- ventral side of the throat will be found the 

 anterior end of the procoracoid cartilage. From the anterior end 

 of this the (1) procoraco-humeralis muscle extends backwards to 

 the proximal end of the humerus. It is small and slip-like in 

 character and serves to draw the limb forward. 



The space between the two procoraco-humerales is occupied 

 by (2) the broad sternohyoid muscle, its fibres in front being 

 inserted upon the hyoid arch and forming the fascia to which 

 the geniohyoid (supra) is attached. Posteriorly the sterno- 

 hyoid is in part attached to the shoulder-girdle, while another 

 portion continues backwards along the ventral surface of the 

 body as the abdominal muscles (vide infra). 



The pectoralis muscles (3) are fan-shaped. Each arises 

 from the mid-ventral line, the posterior portion being continuous 

 with the rectus abdominis muscles to be noticed later. The 

 fibres converge upon the proximal ventral end of the humerus. The 

 pectorales serve to draw the shoulders ventrally and backwards. 



Cut across one of the pectorales in front, turn it back, and 

 see (4) the supracoracoid muscle extending from the coracoid 

 cartilage, between the two shoulders, to the humerus. 



On the side of the body dorsal to the attachment of the fore 

 limb is (5) the latissimus dorsi muscle, a broad sheet whose fibres 

 converge ventrally upon the dorsal surface of the humerus. In 

 front of this and between it and the procoracoid are several 

 muscles as follows: 



Just in front of the latissimus dorsi is (6) the dorsalis scapulae, 

 arising from the dorsal portion of the scapula and inserted, 

 beside the others, upon the humerus. Next in order is (7) the 



