31 



superficialis, and are evidently portions of the latter muscle, though 

 they are named the musculi interbranchiales. 



Above the constrictor superficialis, lying on the side of the 

 neck between it and the dorsal musculature, is a broad trapezius 

 muscle. It arises from the fascia covering the lateral surface of the 

 dorsal musculature. Its fibres pass obliquely downward and back- 

 ward, mediad to the posterior gill-pouches, to insert upon the an- 

 terior edge of the scapular portion of the pectoral girdle. The 

 anterior portion of the trapezius is also inserted upon the epi- 

 branchial of the fifth gill-arch. 



Just in front of the mouth is a pair of strong muscles (levator 

 labialis superioris) , each arising from the ventral surface of the 

 cranium close to the median line. They pass into strong tendons 

 which are inserted among the fibres of the ventral portion of the 

 adductor mandibulae. The muscle mass in front of the mouth and 

 the lower part of the adductor mandibularis thus form the two 

 bellies of a digastric muscle, with the tendon between them. 



* Remove the ventral portions of the first and second superficial 

 constrictors and clear the mass of muscles lying between the coracoid 

 portion of the pectoral girdle and the mandible. Immediately in 

 front of the girdle are two large muscles, the coraco-arcuales com- 

 munes, whose fibres run inward and forward. These muscles 

 cover the ventral surface of the pericardium, to the wall of which 

 their median fibres are attached, while the lateral fibres are at- 

 tached around the ventral ends of the gill-arches. 



In front of the coraco-arcuales communes are three large longi- 

 tudinal muscles. The median, unpaired one, arising from the fascia 

 between the coraco-arcuales communes and inserted upon the pos- 

 terior surface of the lower jaw, is the cor aco -mandibularis. The 

 other two, which lie dorsal to and outside of the coraco-mandibu- 

 laris, are the coraco-hyoidei. They arise from the fasciae covering 

 the anterior ends of the coraco-arcuales communes and posterior 

 parts of the coraco-branchiales, and insert upon the basihyal. 



Dissect out the coraco-mandibularis and coroaco-hyoidei, noting 

 particularly the form and place of origin of the latter. Dorsal to 

 the coraco-hyoidei are the first divisions of the right and left 

 coraco-branchialis muscles, which arise from fascia covering the 

 anterior ends of the coraco-arcuales communes, and are inserted 

 upon the ventral extremity of the ceratohyal cartilage. Notice that 

 they pass dorsad to the anterior branches of the aorta, and that 

 the aorta itself can be exposed between them. 



Remove the coraco-arcualis communis by dissecting it from 

 the pectoral girdle and reflecting it forward. The other four 

 divisions of the coraco-branchialis are now revealed, attached to the 

 lateral surface of the pericardium and the lateral portion of the 

 coracoid. The divisions of the muscle are clearly separated only 

 near their insertions. The second, third, and fourth coraco-branch- 

 ials are attached to the hypobranchial cartilages of the second, third 

 and fourth visceral arches. The fifth division is inserted upon the 

 lateral portion of the basibranchial and the expanded medial end 

 of the fifth ceratobranchial. 



The first aortic branch passes ventral to the first coraco-branch- 

 ial. The second aortic branch passes between the first and second 



*The coraco-mandibularis, coraco-hyodeus, coraco-arcualis com- 

 munis, and coraco-branchialis muscles should be dissected as a pre- 

 liminary operation to following the ventral aorta and its branches. 



