100 SKELETON OF MAMMALIA. 



of fatty tissue. The Skeleton of Mammals always shows in its 

 conformation a great analogy with that of Man (ANIM. PHYSIOL. 

 616 649). The differences which are remarked amongst the 

 various animals of this class, depend essentially ; First, on the 

 absence of abdominal members in the fish-like Mammalia, such 

 as the Porpoise, and the Whale, which Zoologists have included 

 in the order Cetacea ; Secondly, in the diminution of the 

 number of fingers, and in the absence of the Clavicle, amongst 

 the greater number of those species whose members serve only 

 for walking ; Thirdly, in variations in the number of Verte- 

 brae, especially in the dorsal and caudal regions; Fourthly, in 

 the inequalities in the relative sizes of the same bones. 



81. Conformation of the head. The shape of the bony part 

 of the head varies much, according as the face is more or less 

 extended, or the skull developed in a greater degree ; and the 

 study of these differences in proportion is not without interest ; 

 for as we have already seen, there exists, in general, a very direct 

 connection between the degree of intelligence with which an 

 animal is endowed, and the relative size of that portion of its 

 skull which contains the brain. The further we remove from 

 Man, we see the cranium diminish, the jaws and the nasal cavi- 

 ties become more extended ; the orbits are directed more and 

 more outwards, and become less and less distinct from the tem- 

 poral fossae; and finally the occipital foramen, (the aperture which 



gives a passage to the 



& I O 



spinal marrow,) and 

 the two condyles by 

 which the head is 

 connected with the 

 vertebral column, in- 

 stead of being placed 

 towards the middle 

 of the inferior sur- 



FIG. 52. SKULL OF HORSE ; oc, occipital bone ; t, tern- face of the Cranium 

 poral ; /, frontal ; n, nasal ; m, superior maxillary ; im, 

 intermaxillary; mi, inferior maxillary ; o, orbit; t, in- are carried further 



and further back, and 

 end by occupying the posterior aspect of it. So that the jaws, 



