40 OCCIPITAL SEGMENT, OR VERTEBRA. 



retains mucli of tlie shape of the parts so called in the 

 trunk. Nevertheless, the elements of the neural arch of 

 this hindmost segment of the skull have undergone so 

 much development and modification of shape, that they 

 have received special names, and have been enumerated 

 as so many distinct and particular bones. The centrum, 

 No. 1, is called "basioccipital;" the neurapophyses, No. 

 2, " exoccipitals ;" the neural spine, No. 3, " superoccipi- 

 tal;" the diapophyses. No. 4, " paroccipitals." In the 

 human skeleton all those parts are blended together into 

 a mass, which is called the " occipital bone." 



The entire segment, here disarticulated, in the cod-fish, 

 is called the " occipital vertebra," and in it we have next 

 to notice the widely expanded inferior or haemal arch. 

 This consists of three pairs of bones. The first pair are 

 bifurcate, and have two points of attachment to the neural 

 arch, the lower prong, answering to what is called the 

 "head of the rib," abutting upon the neurapophysis ; the 

 upper prong, answering to the "tubercle of the rib," 

 articulating to the diapophysis. The second pair of bones 

 are long and slender, and represent the body of the rib. 

 The first and second piece together answer to the element 

 called " pleurapophysis ; the third pair of bones are the 

 " liEemapophyses ;" these support diverging appendages 

 consisting of many bones and rays. The special names 

 of the above elements of the haemal arch of the occipital 

 vertebra are, from above downwards, " suprascapula," 

 No. 60 ; " scapula," No. 51 ; " coracoid," No. 52. The in- 

 verted arch, so formed, encompasses, supports, and pro- 

 tects the heart or centre of the h^mal system ; it is called 

 the " scapular arch." There are animals — the gymnotho- 

 rax and slow- worm, e. g. — in which this arch supports no 

 appendage; there are fishes — the^)?'oto^:>^!e?'?/s, e.g. Fig. 32 — 



