202 EDWARD PHELPS ALLIS, JUN. 



the external surface of tlie adductor mandibulse muscle, 

 passes into the mandible, lying superficial to the ramus 

 mandibularis trigemini, and ends in the lateral and ampuUary 

 sense organs it innervates. 



Beyond the point where the ramus mandibularis externus 

 is given off by the truncus hyoideo-mandibularis the remaining 

 portion of the truncus separates into three principal branches, 

 and one or more smaller ones. The smaller ones go to the 

 general tissues of the region. One of the three larger and 

 principal parts runs at first downward and backward, and 

 acquires a position on the external surface of the posterior 

 portion of the adductor mandibulfe. It then turns forward 

 and mesially, and passes from the outer surface of the 

 adductor on to that of the muscle CsVo, where it gradually 

 disappears. A second one of the three principal parts runs 

 directly backward, immediately lateral to the dorsal end of 

 the ceratohyal, and near the hind edge of that element turns 

 downward, internal to the muscle Csvo, and around the hind 

 end of the mandibular cartilage. It then runs forward and 

 mesially between the superficial and deeper layers of Csv2, 

 to both of which it sends branches, apparently innervating 

 them. Anteriorly it lies immediately internal to the inter- 

 mandibularis muscle, and there anastomoses completely with 

 that branch of the mandibularis trigemini that pierces the 

 intermandibularis from its outer surface. This anastomosis 

 is, as already stated, the undoubted homologue of the one 

 found in Amia of the ramus hyoideus facialis, with the branch 

 r.ghi of the maxillaris inferior trigemini. 



These two principal branches of the truncus facialis of 

 Mustelus thus form the ramus hyoideus of Stannius' descrip- 

 tions (69, p. 65). 



The third and remaining part of the truncus facialis of 

 Mustelus turns downward, forward, and mesially between the 

 ceratohyal and the mandibular cartilage, and closely accom- 

 panies the pseudobranchial artery as far as that artery 

 extends. Continuing forward beyond the artery, internal to 

 the mandibular cartilage, and near its ventro-mesial edge, it 



