176 EDWAED PHELPS ALUS, JUN. 



upside down, its leg representing a part of the muscle that 

 first runs inward, and then upward and backward along the 

 outer surface of the hind edge of the levator maxillae 

 superioris, to have its origin with that muscle from the 

 skull, as Tiesing describes for his muscle Csdjy. The pos- 

 terior arm of the inverted T iiins backward above the 

 spiracle, and has its origin on the fascia there as Tiesing 

 describes. The anterior arm of the inverted T is the re- 

 tractor palpebra) superioris of Tiesing. Nerve fibres could 

 not be definitely traced to these muscles, but they would 

 seem to be most unquestionably innervated by branches of 

 the same nerve that innervates the levator maxilla; superioris, 

 as Tiesing states. The posterior head of the deeper muscle 

 might, however^ easily receive fibres from that branch of the 

 facialis that innervates Csd^. 



Beyond this large and largely motor branch no branch is 

 given off by the ramus mandibularis until after it separates, 

 as already described, from the truncus buccalis-maxillaris 

 just before that truncus passes outward from the floor of 

 the orbit on to the lateral surface of the muscle Add/3. 

 Running laterally across the dorsal edge of the palato- 

 quadrate cartilage, the ramus mandibularis reaches the 

 dorsal edge of the antero-dorsal corner of the adductor 

 mandibulas. There the larger part of the nerve turns down- 

 ward and backward along the outer surface of the adductor, 

 lying iu a groove between that muscle and the muscle 

 Add/3. 



As the ramus mandiljularis here turns downward and back- 

 ward it gives off a large branch, which, separating into two 

 parts, sends one branch forward and downward into the 

 anterior portion of the muscle Add/3, and another back- 

 ward and downward into the posterior portion of the same 

 muscle. This is, accordingly, the motor nerve of the nuiscle 

 Add/3, and it is certainly in niy embryo a branch of the ramus 

 mandibularis, and not a branch of the ramus nuixillaris. Both 

 Stannius (59) and Tiesing (62) find this muscle innervated by 

 a branch of the ramus ujandibularis in the selachians examined 



