2o8 ALUS. [Vol. XVIII. 



the posterior process of the squamosal. It runs downward and 

 backward along the antero-ventral edge of the trunk muscle, 

 passes external to the nerve of the lateral line, and is inserted in a 

 tendinous membrane that lines the inner surface of the mucous 

 membrane that forms the hind wall of the gill chamber. This 

 membrane covers and is attached to the dorsal end of the antero- 

 lateral face of the clavicle. The muscle, in the one specimen in 

 which it was examined, was innervated by a branch of the third 

 vagus that arose from the ganglionic swelling of the nerve. It is 

 shown in Fig. 59 with a small section of the muscle attached. 



The Interarcuales Dorsales are nine in number, three inter- 

 arcuales dorsales, three obHqui dorsales, two transversi dorsales 

 and a retractor arcuum branchialium. To these nine muscles 

 should be added a ligament that probably represents the inter- 

 arcualis between the hyoid and first branchial arches, and also a 

 partly differentiated muscle that seems to represent the inter- 

 arcualis between the fifth arch and an arch that formerly existed 

 posterior to it. 



The first interarcualis dorsalis (lad. I.) is a ligament that 

 arises (Fig. 11) from the lateral surface of the petrosal immedi- 

 ately dorsal to the surface of origin of the external levator of the 

 first arch. It runs downward and slightly backward along the 

 external surface of the external levator of the first arch, and is 

 inserted along the antero-lateral edge of the first epibranchial, 

 near its proximal end, and on the corresponding edge of the 

 first infrapharyngobranchial, near its distal end. It usually breaks 

 up into several parts near its insertion. It lies internal to, and 

 hence morphologically in front of, the ramus anterior of the 

 glossopharyngeus. 



The second interarcuaHs dorsalis (/ad. //.) arises (Fig. 29) from 

 the antero-lateral edge of the second epibranchial, opposite the base 

 of the suprapharyngeal process of that bone. It runs forward 

 and slightly inward and is inserted on the postero-mesial edge 

 of the first epibranchial at the base of the suprapharyngeal process 

 of that bone. It is a small muscle, largely tendinous, and is 

 apparently innervated by branches of a plexus of delicate nerves 

 that spread over its dorso-external surface, the nerves arising 



