MUSCLES AND ENDOSKELETON 51 



proceed from the support of the fin. The claspers of the 

 males are closely connected with the posterior part of the 

 hind-fin and have a complex cartilaginous skeleton. 



The pectoral girdle forms an almost complete hoop of 

 cartilage which is attached dorsally to the vertebral plate. 

 The ventral region is the cora^oid bar and is separated 

 from the dorsal or scapular processes by three facets to 

 which the three pieces of the pectoral fin are attached. 

 The anterior piece is the propterygium ; the very small 

 median piece, the mesopterygium ; and the posterior piece, 

 the metapterygium. All of these and a part of the girdle 

 bear jointed radials, parts of the endoskeleton. 



B. The Skull and Visceral Skeleton. 



The chondooranium is the cartilaginous case inclosing 

 the brain. At the anterior end is the rostrum and the orbit 

 which hold the eye in at one side. On the dorsal surface 

 are two large anterior fontanelles and on either side of 

 the rostrum is an olfactory capsule. The chondocranium 

 also has a foramen magnum for the entrance of the spinal 

 cord, auditory capsules inclosing the ears, olfactory cap- 

 sules, nasal capsules, and two occipital condyles, articulat- 

 ing with the first vertebra. 



The splanchnocranium or visceral skeleton supports the 

 gills. It consists of several gill-arches. Two are much 

 modified in connection with the jaws. The first gill-arch, 

 the mandibular arch of the upper jaw, is a strong trans- 

 verse bar formed by the union of two pterygoquadrate 

 cartilages. The lower jaw is formed by the union of two 

 Meckel's cartilages. The second or hyoid is a slender arch 

 with a ventral median basihyal, a ceratohyal on each side 

 of the basihyal, and dorsal to these the hyomandibular. 

 This articulates with the otic region of the skull and acts 

 as a suspensor of the lower jaw. 



