THE ELASMOBRANCH FISHES 



193 



ward on the cord. The ramus ventralis passes to the inidventral line where it 

 enters the arteria spinalis (a.sp.). Branches, especially from the tractns la- 

 teralis, enter the substance of the cord and terminate in large part around the 

 grey matter (Sterzi, 1904) . Other branches given off laterally from this dorsal 

 branch of the segmental pass outward in a spiral direction along the myosep- 

 tum dorsally and laterally to the muscle bundles. 



The segmental, as the intercostal (i., fig. 180), 

 is continued laterally to supply the musculature 

 encircling the peritoneum. The intercostals in all 

 recent Elasmobranchs are reduced in number (fig. 

 177) . While in Heptanch us there are about thirty 

 pairs, in the rays they may be reduced to only a 

 few pairs, and those remaining may present great 

 irregularities in size and position. This irregu- 

 larity is especially noticeable in the trunk region 

 where there is a considerable crowding of the vis- 

 cera. 



The most ventral branch of the segmental, the 

 renal artery (rn.), turns ventrally and enters the 

 tissue of the kidney. In the posterior region where 

 the kidney is enlarged the vessels come to be strong 

 trunks which pass downward, then sharply back- 

 ward, to break up into numerous branches. 



The renal divisions of the segmental artery may 

 be modified as the oviducal arteries. In Scyllium 

 several pairs of the segmentals just posterior to 

 the subclavians {od.a., fig. 177a) pass to the ovi- 

 duct and shell glands. The fourth to the sixth are 

 the main ones, which pass to the oviduct and along 

 the greater part of its length. In Heterodontus 

 francisci two sets of these arteries are present. An 

 anterior set arises from the eleventh and twelfth 

 segmentals, and a posterior set from the nine- 

 teenth and twentieth segmentals. The oviducals 

 anastomose on the oviduct and in viviparous types 

 send arteries to the inner lining of the uterus to 

 supply the villi. In those forms in which the young 

 are carried for a considerable time the oviducal 

 arteries may be remarkably developed [Acanthias, see p. 306, fig. 267a ; 

 Rhinohatis) . 



CAUDAL SEGMENTALS 



Fig. 180. Transverse section 

 through trunk region, Squalus 

 sucklU, showing branches of 

 a segmental artery, (From 

 Coles.) 



C, central muscle bundle ; 

 c, artery to central bundle; 

 d.a., dorsal aorta ; DMS., dor- 

 somedial septal bundle of 

 muscles; dms., dorsomedial 

 septal artery; DS., dorsal sep- 

 tal bundle; ds., dorsal septal 

 artery; d.vm., dorsal verte- 

 bromuscular artery; i., inter- 

 costal artery ; L., lateral 

 bundle ; Ja.v., lateral abdomi- 

 nal vein ; U., lateral line ; N., 

 neural muscle bundle ; n., ar- 

 tery to neural buiidle ; rn., 

 renal artery; vs.a., vertebro- 

 spinal artery. 



The segmentals in the region of the tail differ somewhat from those of the body 

 just described. The principal change is the result of the haemal arch. The 

 segmental, in addition to sending a vertebromuscular branch upward, sends 



