374 THE DOGFISH LESS. 



The entire skeleton consists of separate pieces of cartilage, 

 calcified or not, and connected with one another by sheets 

 or bands of connective tissue called ligaments : it is divisible 

 into the following parts : 



A. The skull or skeleton of the head, consisting of 



1. The cranium or brain-case, enclosing the brain 



and the chief sense-organs. 



2. The upper and loiver jaws. 



3. The visceral arches, a series of cartilaginous hoops 



supporting the gills. 



B. The vertebral column or " backbone," a jointed axis ex- 



tending from the cranium to the end of the tail, 



and enclosing the spinal cord, 

 c. The skeleton of the median fins. 

 D. The skeleton of the paired fins, consisting of 



1. The shoulder-girdle or pectoral arch, to which are 



attached 



2. The pectoral fi ns. 



3. The hip-girdle or pelvic arch, to which are at- 



tached 



4. The pelvic fins. 



The cranium (Fig. 100, Cr) is an irregular cartilaginous 

 box containing a spacious cavity for the brain, and pro- 

 duced into two pairs of outstanding projections : a posterior 

 pair, called the auditory capsules (aud. cp\ for the lodgment 

 of the organs of hearing, and an anterior pair, the olfactory 

 capsules (olf. cp\ for the organs of smell. Between the 

 olfactory and auditory capsules, on each sidej the cranium 

 is hollowed out into an orbit (or) for the reception of the 

 eye. In front the cranium is produced into three cartila- 

 ginous rods (r), which support the snout. On its posterior 



