22 MORPHOLOGY OF THE VERTEBRATA. 



PECTORAL ARCH 



Consists of the clavicles, long knife-like bones, pointed below, 

 where they meet each other in the middle line, and connected 

 together by ligament. Attached to their dorsal end is another 

 smaller bone, the supraclavicle, which articulates with another 

 bone forked in front — the post-temporal: one fork of which is 

 connected with the epiotic, and the other to the pterotic. 



Attached to the back of the clavicle are two small bones, above 

 the scapula, and below coracoid ; articulating with these are five 

 basal cartilages, to which the fins are attached. The clavicle gives 

 attachment to a styliform bone, the post clavicular, which runs 

 back among the lateral muscles. 



SKULL. 



As the arrangement of the various bones of the skull can be 

 readily seen by a glance at the accompanying plate, we only 

 purpose to draw attention to the most important points concerning 

 them. 



The articular cup in the basioccipital for the atlas is a deep 

 conical excavation. 



The homologue of the suspensorium of the dog-fish ossifies so- 

 as to give rise to two bones: an upper broad hyomandibular, 

 with which the sperculum articulates; and a low style-shaped 

 bone — the sympletic— which is firmly held into a groove on the 

 posterior inner suface of the quadrate. 



Meckel's cartilage persists throughout life, but its proximal end 

 is ossified into the os articulare of the lower jaw. 



On the under surface of the skull are two membrane bones — the 

 vomer in front, and the large parasphenoid behind, which covers 

 in all the base of the cranium from the basioccipital to the vomer. 



The ethmoidal cartilage remains unossified. 



The opisthotic is a distinct bone, and the prootic well 

 developed, being placed in front of the anterior vertical semi- 

 circular canal, and behind the exit of the third nerve. 



The maxillae take but little share in the formation of the gape, 

 which is bounded by the backwardly extended premaxillse above. 



The palato-quadrate arch is represented by the palatine in front, 

 and the quadrate behind. In addition to these is an external 

 ectopterygoid, an internal entopterygoid, and a metapterygoid, 

 which envelopes the upper and posterior part of the primitive 

 quadrate cartilage. 



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