THE DOGFISH 9 



is connected with the second by a median plate, the anterior 

 basibranchial; and that a posterior basibranchial occurs farther 

 back. With what are the other hypobranchials connected? 

 What are the peculiarities of the pharyngobranchials of the 

 fourth and fifth arches? 



Draw the whole visceral skeleton from the side and from the 

 ventral surface, natural size. 



The pectoral girdle or shoulder-girdle is the U-shaped arch 

 of cartilage which supports the anterior pair of fins. It is com- 

 posed of halves united by ligament in the mid-ventral line. Is 

 there any articulation between the pectoral girdle and the axial 

 or branchial skeleton? At about the middle of each half of the 

 girdle is a glenoid surface for the articulation of the skeleton of 

 the fin. This divides the girdle into dorsal (scapular) and ventral 

 (coracoid) regions, the upper portion of the scapular region being 

 a distinct suprascapular cartilage. Close to and hardly below 

 the glenoid surface is a foramen for the passage of nerves to the 

 fin, while behind, the coracoid gives off a strong coracoid process. 



In the skeleton of the fin make out three cartilages (basalia) 

 which articulate with the glenoid surface; in front a propterygium, 

 a middle mesopterygium, and a posterior metapterygium, the 

 middle one being much the larger, and undivided, while the others 

 are transversely divided (into how many elements?). All three 

 basalia bear several cartilaginous radialia or fin-rays, while the 

 distal portion of the fin is supported by numerous horny threads 

 or actinotrichia. Are any of the radialia jointed? 



Draw the girdle from the side, and the fin from above, natural 

 size. 



The pelvic girdle supports the hinder pair or ventral fins. 

 It consists of a transverse cartilage bar which projects slightly 

 on the dorsal superior surface as an iliac process. Just medial 

 to this process the bar is perforated by two foramina, the medial 

 of these being the obturator foramen for the passage of the nerve 

 of the fin. On the lateral posterior angle of either side are the 

 large acetabular facets for the articulation of the skeleton of 

 the fin. 



The skeleton of the fin consists of two basal portions which 

 bear a number of slender cartilaginous radialia, and these are 

 continued by numerous actinotrichia, as in the pectoral fin. The 

 anterior basale, the prebasale, projects almost laterally from the 



