1910.] ANATOMY OF THE FRILLED SHARK. 565 



extent on the terminal cartilage T.v. In the greater part of its 

 extent it forms the inner lip bounding the channel. 



Muse, compressor, S. — On the dorsal side this muscle appears 

 to arise from the outer side of /3. It really has its origin on the 

 outer side of the proximal end of the axial cartilage b, lying 

 beneath /3. Contributing largely to it also on its outer side are 

 muscle-bundles belonging to the last elongated lateral radials. 

 These bundles belong to the system of dorsal radial muscles (0) 

 which arise from the body-wall. The last elongated radial 

 carries a portion of the muse, compressor on its inner side, thus 

 forming the outer lip bounding the channel. On the ventral 

 side the muse, compressor takes the form of a somewhat 

 oval sa,c whose cavity communicates with the channel on the 

 dorsal side of the appendage, and whose lining is of epithelium, 

 continuous with that covering the appendage. Its tapering 

 anterior end is attached to the aponeurosis below the last ventral 

 radial muscle, whilst distally it is connected by loose soft tissue 

 with the terminal cartilage T.v. From the disposition of the 

 whole muscle and from its relation to the other muscles of the 

 appendage, I regard it as derived from modified muscle-bundles 

 of the last two or three radials. This view is in agreement with 

 Huber's, according to which the musculature of the muse, com- 

 pressor has originated from modified radial muscle-bundles of the 

 last few radials. 



Radial muscles. — On the dorsal side there are the muscle- 

 bundles 0, which have their origin in a lateral aponeurosis 

 running along the lower ends of the myomeres of the body-wall. 

 In removing these muscles it is found that they are indistinctly 

 divided into two layers, a superficial one reaching as far as the 

 horny fibres of the fin and a deeper layer which does not extend 

 quite as far outward. 



On the ventral side there are the radial muscles Ra, which 

 originate on the pelvic girdle close to the median line and extend 

 outward to the horny fibres. Toward the anterior end the 

 separate bundles have fused together, thus corresponding with 

 the fusion of the radials above them. 



m. Skeleton. 



The following account is based on the dissection and exami- 

 nation of the copulatory appendage of the right side, and on a 

 careful comparison made with this and the appendages from 

 another specimen in the museum here. 



The only previous accounts of the mixipterygia of Chlamydo- 

 selachus are those given by Giinther (14), quoted by Jungersen 

 (21) and by Braus (3). The mixipterygium figured by Braus is 

 very different from that given by Giinther or that given in 

 fig. 22 in the present paper. It appears to be in an undeveloped 

 condition, for it is small and no terminal cartilages are shown. 



