THE SKATE. 69 



164. The fibrous partition continued from the outer face, 

 of the branchial arch, and supported by the cartilaginous 

 branchial rays. 



165. The soft vascular branchial filaments covering 

 both sides of the partition, to which they are firmly connected 

 along almost their whole length, their outer extremities only 

 being free. 



166. The afferent branchial artery, running along the outer face of 

 the branchial arch, in the middle line : it is of considerable size at the 

 ventral end of the gill, but gradually diminishes towards its dorsal 

 end. 



167. The efferent branchial arteries, two trunks smaller than the 

 afferent vessel, and running along the lateral edges of the arch, at the 

 bases of the rows of filaments. They are of considerable size at the 

 dorsal end of the arch, and dimiuibh somewhat towards its ventral 

 end. 



168. The thymus glands are exposed by the removal of the gills : 

 each is a whitish body, about an inch long, lying immediately dorsal 

 to the pharyngo-branchials. 



C— SPECIAL DISSECTION OF THE NERVOUS 

 SYSTEM AND SENSE ORGANS. 



XL. It is advisable to take a fresh skate for the nervous 

 system, at least unless the subject used for the 

 foregoing work has been well preserved in strong 

 spirit. The viscera, with the exception of the 

 kidneys and vasa deferentia, may be removed at 

 once. 

 Expose the brain and anterior part of the spinal cord, 

 as directed in § XV., p. 46. If a preserved brain is 

 not available, the verification of the description of 

 the ventral surface must be left until the origins of 

 the nerves have been made out (§§ 179 — 189) when 

 the brain may be removed. Observe the following ;— 



