ii.] THE SPINAL SKELETON'. 



47 



though less developed, in the posterior cervicals of the 

 Great Auk. 



The articular surfaces which support the ribs in man are 

 normal in his class. Sometimes, however, each vertebra 

 carries but one surface that for the head of the rib (as in 

 the Dolphin). The two articular surfaces may coexist at 

 different levels on one single process, as in the dorsal verte- 

 brae of the Crocodile ; or they may be in close apposition, 

 and, as it were, fused together, as in Serpents ; or they may 

 be raised on two quite distinct processes one dorsal, the 

 other ventral as in the Ichthyosaurus and in Menobranchus. 



We find in some serpents peculiar processes (Fig. 59, t$) 

 extending ventrally and pre-axially from the base of the 

 inner side of the transverse processes. 



The even surface of the anterior (ventral) aspect of the 

 dorsal vertebrae of man is very different from what we find in 

 some animals, as e.g. the Penguin, Cormorant, and many 

 serpents, where there are long hypapophyses equalling or 

 exceeding the neural spines in length. 



24. The CERVICAL VERTEBRAE of man, in that they are 

 seven in number, conform to a law which is singularly con- 

 stant in his class, whatever the length of the neck, whether 

 it be extremely long, like that of the Giraffe, or like that of the 

 Porpoise, reduced to a minimum. Nevertheless, this law is 

 not absolutely universal, as there are one or two singular 

 exceptions amongst Mammals. Thus the Three-toed Sloth 

 has nine cervical vertebras, while one of the Two-toed kind 

 (Cholcepus Hoffmannii] and the Manatee have but six. 



In Sauropsidans the number is greater, and sometimes 

 there are as many as twenty-five, as in the Swan. In Batra- 

 chians but a single vertebra can be called cervical, and 

 none merit the name in the class of Fishes. Nevertheless, 

 the first three or four vertebras next the head may, in some 

 fishes, present a marked difference from those vertebrae 

 which succeed, being much elongated and all united by 

 suture, as in Fistularia and JBagrus, and they may, as in the 

 latter fish, develop a continuous hypapophysial canal. The 

 second and third vertebras may form a hollow bladder-like 

 case of bone, as in Cobitis, or send outwards or downwards 

 special processes, as in the Carp. 



In that the cervical vertebras of man are smaller than 

 those in the other regions, he agrees with many animals and 

 differs from many. They may be (as in Bats and in their 

 extinct precursors, the Pterodactyles) absolutely larger in all 



