132 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



The homology of these muscles with those of mammals is somewhat doubtful. 

 Some suggestions are given by W, page 229. A figure which may aid in identify- 

 ing the muscles will be found in W, page 228. 



3. The muscles of the pectoral girdle and fore limb. — Study the ventral 

 surface of the pectoral girdle. Covering the coracoid cartilage is a fan-shaped 

 muscle, the supracoracoideus, inserted on the humerus. On either side, overly- 

 ing the elongated procoracoid cartilage, is the procoracohumeralis , inserted on the 

 humerus just anterior to the preceding. Behind the supracoracoideus and 

 practically continuous with it is the large fan-shaped pectoral muscle, which 

 originates on the linea alba and some of the myosepta. Covering the ventral 

 surface between the two procoracohumerales, is the broad sternohyoid muscle, 

 differentiated out of the ventral portions of the most anterior myotomes. At its 

 anterior end the two halves of the sternohyoid muscle fork, another pair of 

 muscles (geniohyoids) being inserted between the two parts of the fork. The 

 sternohyoid should be traced posteriorly; it has some attachments to the 

 pectoral girdle, passes dorsal to the pectoral muscles which should be lifted to 

 see it, and becomes continuous with the rectus abdominis. The sternohyoid 

 and rectus abdominis preserve almost perfectly the segmented condition. 



On the dorsal side of the pectoral girdle identify the latissimns dorsi, the most 

 posterior and largest of the dorsal girdle muscles. It originates by about five 

 separate slips from the myosepta of adjacent myotomes, and these slips converge 

 to the humerus. This muscle illustrates very well the compound origin of 

 limb muscles by slips or buds from several myotomes. Anterior to the latissimus 

 dorsi and covering the surface of the scapula is the dorsalis scapulae, also inserted 

 on the humerus. Anterior to this is the trapezius (or cucullaris) originating by 

 two slips or heads and inserted on the scapula. Between the trapezius and the 

 procoracohumeralis is the omohyoid muscle, running parallel to the latter, from 

 the hyoid to the girdle. Cut through the middle of the latissimus dorsi and 

 find beneath it the typical myotomes. These become in higher forms the 

 serratus muscle. 



In the upper arm identify on the ventral side two muscles: an anterior one, 

 the biceps, extending from the humerus to radius; and a posterior coracobrachial 

 originating from the coracoid cartilage and passing to the distal end of the 

 humerus. The dorsal side of the upper arm is occupied by the large triceps 

 muscle, with origins on coracoid, scapula, and humerus, and insertion on the 

 ulna. The muscles of the forearm are in two chief masses, a dorsal extensor 

 which extends the hand and a ventral flexor which bends the hand. 



4. The visceral and head muscles.— The visceral muscles or muscles of the 

 gill arches are considerably modified in relation to the greater separation of head 

 from trunk and the degeneration of the gill arches. Skin the head completely. 

 Across the ventral surface from one half of the lower jaw to the other passes 

 the mylohyoid muscle. It originates on the jaws and is inserted on the median 



