212 ALUS. [Vol. XVIII. 



mouth. The muscle fibers themselves are not here inserted directly, 

 either on the skin, or on the membrane, for the membrane can be 

 removed from the muscle wdthout tearing it. The dorsal, sucker- 

 like membrane can not be so removed without cutting the muscle 

 fibers. The muscle bulges downward in the middle line, a longi- 

 tudinal median ridge being thus formed on its ventral surface. 

 The muscle crosses dorsally the anterior end of the third obliquus, 

 and its anterior edge lies immediately posterior to the transverse 

 groove, already described, that connects, on the roof of the mouth, 

 the anterior end of the branchial cleft that lies between the hyoid 

 and first branchial arches of one side of the head with the cor- 

 responding cleft on the opposite side. The muscle is innervated by 

 branches of the nerve that innervates the second and third 

 obliqui. 



The Transversus Dorsalis Posterior (Tdp) arises from the 

 posterior portion of the dorsal surface of the proximal articular 

 head of the third epibranchial, and from the dorsal surface of the 

 third infrapharyngobranchial anterior to the mesial end of that 

 epibranchial, the latter surface of insertion lying mesial to the 

 posterior end of the ridge along the middle of the dorsal surface 

 of the infrapharyngobranchial. The fibers of the muscle all run 

 across the middle line of the head to the corresponding surfaces 

 on the opposite side. The muscle, like the anterior transversus, 

 is much wider in the middle than at its ends, its anterior edge 

 projecting strongly forward in the middle line of the head, while 

 its posterior edge has a wavy outline, projecting backward at 

 first and then slightly forward in the middle line. The lateral 

 ends of the muscle lie ventral to the posterior ends of the third 

 obliqui. Its middle part lies dorsal to the anterior ends of the 

 retractores arcuum branchialium dorsales. From the hind edge of 

 the muscle, near the middle line, a small bundle of fibers runs lat- 

 erally and backward on each side, and joins and fuses with the 

 constrictor of the oesophagus. The muscle is innervated by a 

 branch of the nerve that innervates the third obliquus. 



The Retractores Arcuum Branchialium Dorsales (Rbad) 

 are two in number, one on each side of the head, instead of but a 

 single muscle as in Aiiiia. The muscle, on each side, arises from 

 the ventro-lateral surface of the third and fourth vertebrae, runs 



