SKELETON 



33 



with the trabeculae, which surround a basicranial fontanelle. It 

 is through this aperture that the large pituitary sac passes down- 

 wards and backwards from above to expand below the brain- 

 case. The trabeculae fuse in front below the pituitary sac, 

 expand into a wide plate, and become continuous with a lateral 

 subocular arch passing downwards on either side and joining the 

 parachordals behind. At the side, the arch sends down a styloid 

 process ending below in a longitudinal cornual cartilage. In front, 

 the trabecular plate is connected with a large median posterior 

 dorsal plate, overhanging an anterior dorsal plate. These, together 

 with lateral plates, cover and support the anterior buccal region in 

 front of the nostril. The sucker surrounding; the mouth, and armed 



'" a y up r V 



Fig. 19. 



Tail of Myxine glutinosa, L. , cut so as to show the skeleton and the opening of the intestine, 

 etc. ; left-side view, a, anus ; c, gap behind mesentery leading from right to left coelomic 

 cavities ; d.r, cartilage radials of dorsal median fin ; g, median opening through which the 

 genital cells escape; i, intestine; m.il, dorsal mesentery; m.v, ventral mesentery; », nerve- 

 cord ; nt, notochord ; rk.d, left kidney duct ; u.p, urinary papilla ; v, cartilage radials of ventral 

 median fin ; v.p, cartilaginous plate. 



with epidermal teeth, is strengthened with an annular cartilage, 

 near which are placed a median ventral cartilage and a styliform 

 cartilage on either side (Figs. 17, 20). The rasping ' tongue' itself 

 is supported by large cartilages. 



Behind the auditory capsule, the basal region of the cranium 

 and the styloid processes are continuous with a complex network 

 of cartilaginous bars situated in the wall of the pharynx, surround- 

 ing the gill-slits, and enclosing the pericardium itself. This is the 

 ' branchial basket ' (Fig. 20). 



In the Myxinoidea, both the roof and the side-walls of the 

 brain-case are membranous (Figs. 21, 22, 23). The nasal organ 

 is surrounded by an apparently median cartilaginous capsule, 

 attached by two strips to the trabeculae. Cartilaginous rings, 

 mostly incomplete, surround the long nasal tube. Between the 



