MAMMALS. 567 



The cranial bones are, as in man, connected by suture. The 

 names of the sutures are borrowed from human anatomy. The two 

 parietal bones coalesce in some carnivorous animals, in the bats, 

 in the horse, in the ruminants and rodents, to form a single bone, 

 so that in these there is no sagittal suture. On the other hand, the 

 frontal bone in most mammals is formed of two bones that meet in 

 the mid plane. The number of separate cranial bones is in most 

 mammals less than in reptiles and fishes. As in the rest of the 

 vertebrate animals, four cranial vertebrae may be distinguished. 

 The first or posterior vertebra is formed by the occipital bone. 

 The basilar portion of the occipital bone (the basioccipital OWEN) 

 is the body or centrum (OwEN) of this posterior vertebra; the arti- 

 cular portions (exoccipitals) are the neural arches (neurapophyses), 

 and the occipital part (supra-occipital OWEN) or neural spine is the 

 covering lamina by which the ring is closed above and which often 

 develops a crest. These four parts coalesce in many mammals 

 more slowly than in man to form a single bone. The occipital bone 

 in this class differs from that in the class of birds in there being 

 two articular condyles for connexion with the first cervical vertebra, 

 which lie at the sides of the occipital foramen ; in the birds, on the 

 contrary, and in the Eepitilia haplopnoa, this bone has a single 

 articular tubercle which lies in the middle under the occipital fora- 

 men. The occipital foramen is usually, with the exception of man 

 and the monkeys, situated more at the posterior extremity than on 

 the inferior surface, whence the cranium lies more in the same 

 direction with the cervical vertebrae. In most mammals there is 

 seen on the occipital bone a pyramidal process which is often con- 

 founded with the processus masto'ideus ; it is the descending part of 

 the coalesced par-occipital ; and serves, amongst other uses, for the 

 attachment of the digastric muscle which depresses the lower jaw; 

 it is very long in the hog and the kangaroo, also (though in a less 

 degree) in the horse and the ruminants 1 . 



The second cranial vertebra has for its centrum the posterior 

 part of the body of the sphenoid (basisphenoid OWEN), for its 



1 Processes jugularis or paramastoideus, see HALLMAN Die vergleickende Osteologie 

 des Schlaferibeins, B. 7, 8 ; DUVERNOT names this part apopkysis pyroldea. [It is the 

 parapophysis of the occipital vertebra it is a distinct bone in fishes, but in the rest of 

 the vertebrates is only a process from the ex-occipital, in man the rectus lateralis muscle 

 is attached to it. OWEN Homol. p. 30.] 



