78 THE VERTEBRATE SKELETON. 



The hyomandibular (fig. 6, 13) is a short stout rod of cartilage 

 projecting outwards, and somewhat backwards and downwards 

 from the cranium, with which it articulates behind the orbit 

 and below the postorbital groove. Its distal end articulates 

 with a rather long slender bar, the cerato-hyal (fig. 6, 14), 

 which is in its turn attached to the side of the basi-hyal. The 

 basi-hyal is a broad plate, rounded in front and drawn out 

 behind into two processes to which the two halves of the 

 first branchial arch are attached. The posterior surfaces of 

 both hyomandibular and cerato-hyal bear slender cartilaginous 

 processes, the gill rays. The hyoid arch forms the main 

 suspensorium or means by which the jaws are attached to 

 the cranium. This attachment is chiefly brought about by 

 a series of short ligaments which connect the posterior ends 

 of both upper and lower jaws with the hyomandibular, but 

 there is also a ligament connecting the lower jaw with the 

 cerato-hyal. The attachment of the jaws to the cranium is 

 also partially effected by the prespiracular and ethmo-palatine 

 ligaments. 



(c) Each of the five branchial arches is a hoop, in- 

 complete above and formed of four or more pieces of cartilage. 

 The most dorsal elements, the pharyngo-branchials, are 

 flattened, pointed plates whose free inner ends run obliquely 

 backwards, and terminate below the vertebral column. They 

 are connected at their outer ends with the short broad epi- 

 branchials (tig. 6, 16) which lie at the sides of the pharynx. 

 From the epi-branchials arise the long cerato-branchials 

 (fig. 6, 17) which run forwards and inwards along the ventral 

 wall of the pharynx. The first four cerato-branchials are 

 connected with small rods, the hypo-branchials, which run 

 backwards to meet one another in the middle line. The last 

 two pairs of hypo-branchials and the fifth cerato-branchials 

 are connected with a broad median plate, the basi-branchial. 

 Along the outer sides of the second, third and fourth cerato- 



