136 ZOOLOGY SECT. 



the ventral surface, opposite the interval between the anterior and 

 posterior dorsals (in' Scyllium)] it resembles the latter in size and 

 shape. 



Of the lateral fins there are two pairs, the pectoral and the 

 pelvic. The pectoral are situated at the sides of the body, just 

 behind the head. The pelvic, which are the smaller, are placed 

 on the ventral surface, close together, in front of the middle of 

 the body. In the males the bases of the pelvic fins are united 

 together in the middle line, and each has connected with it a 

 Jasper or copulatory organ. The latter is a stiff rod, on the inner 

 and dorsal aspect of which is a groove leading forwards into a 

 pouch-like depression in the base of the fin. 



The mouth a transverse, somewhat crescentic opening is 

 situated on the ventral surface of the head, near its anterior end. 

 In front and behind it is bounded by the upper and lower jaws, 

 each bearing several rows of teeth with sharp points directed back- 

 wards. The nostrils are situated one in front of each angle of the 

 mouth v , with which each is connected by a wide groove the naso- 

 luccal groove. In Chiloscyllium the outer edge of the groove is 

 prolonged into a narrow subcylindrical appendage the "barbel. A 

 small rounded aperture, the spiracle placed just behind the eye 

 leads into the large mouth cavity, or pharynx. Five pairs of 

 slits running vertically on each side 7)f the neck the branchial 

 slits also lead internally into the mouth cavity. A large median 

 opening on the ventral surface at the root of the tail, between the 

 pelvic fins, is the opening leading into the cloaca, or chamber 

 forming the common outlet for the intestine and the renal and 

 reproductive organs. A pair of small depressions, the abdominal 

 pores, situated behind the cloacal opening, lead into narrow passages 

 opening into the abdominal cavity. 



The skeleton is composed entirely of cartilage, with, in certain 

 places, depositions of calcareous salts. As in Vertebrates in general, 

 we distinguish two sets of elements in the skeleton the axial set 

 and the appendicular, the former comprising the skull and spinal 

 column, the latter the limbs and their arches. 



The spinal column is distinguishable into two regions the 

 region of the trunk and the region of the tail. In the trunk region 

 each vertebra (Fig. 767, A} consists of a centrum (cent.), neural arch 

 (neur.\ and transverse processes (tr.). In the caudal region there 

 are no transverse processes, but inferior or haemal arches (B, haem.) 

 take their place. The centra of all the vertebra are deeply biconcave 

 or ampMccelous, having deep ""conical concavities on their anterior 

 and posterior surfaces. Through the series of centra runs the noto- 

 chord, greatly constricted in the centrum itself, dilated in the large 

 spaces formed by the apposition of the amphicoelous centra of 

 adjoining vertebras, where it forms a pulpy mass. The concave 

 anterior and posterior surfaces of the centra are covered by a dense 



