THE COD. 121 



170. The bony branchial arch, supporting the gill 

 along its whole length, and having a crescentic transverse 

 section. 



171. The form and arrangement of the branchial fila- 

 ments: each has the form of a right-angled triangle with 

 a very narrow base attached to the branchial arch, and with 

 the apex free : the hypotenuses face opposite ways in suc- 

 cessive filaments, so that while the bases of the filaments form 

 a single row, their free ends form a double row, each row 

 corresponding with a demibranch in the skate (p. 46, 84). 



172. The complete freedom of the branchial filaments 

 owing to the absence of partitions, such as are found in the 

 Skate (p. 45, 83, and p. 69, 164, 165). 



173. The afferent and efferent branchial arteries, running 

 parallel with one another along the outer side of the 

 branchial arch, the afferent artery being external : the 

 branches of the afferent artery go to the inner sides (hypo- 

 tenuses, 1 7 1 ) of the gill filaments, the feeders of the effer- 

 ent artery lie along their outer sides. 



XXXII. Keeping the fish in the supine position, dissect away the 

 pharyngobranchials of both sides sj as to expose both epi- 

 branchial arteries ; trace forward the latter, and dissect away 

 enough of the mucous membrane to make out the following : 



174. The carotid arteries (Fig. 32, c), continuing forwards the 

 epibranchial trunks, and uniting with one another above the parasphe- 

 noid by a short, slender, transverse trunk, thus completing the circulus 

 cephalicus. 



175. The hyoidean artery (Ft*. 32, hy), springing from the ventral 

 end of the first afferent branchial, and dividing into two branches, one 

 of which forms the afferent artery of the pseudobranch (/j), while the 

 other anastomoses with the epibranchial (ep.br}. 



The blood is collected from the pseudobranch by an efferent (ophthal- 

 mic) artery (op), which, after curving over the corresponding carotid, 

 and anastomosing with its fellow of the opposite side by a short trans- 

 verse trunk immediately in front of the carotid anastomosis, passes to 

 the choroid gland of the eye ( 178). 



