22 THE SKELETON OF THE CAT. 



cranial, and lies craniad of the latter; it encloses the nasal 

 cavity. It contains the following thirteen bones: two pala- 

 tines, one vomer, two maxillaries, two lachrymals, two pre- 

 maxillaries, two nasals, two malar or zygomatic bones. The 

 two halves of the mandible or lower jaw are frequently included 

 in the facial portion of the skull, making in all fifteen separate 

 bones in this part of the skull. 



In the following the bones of the skull are first described 

 separately, then an account is given of the skull as a whole. 



Occipital Bone. Os occipitale (Figs. 17 and 18). The 

 occipital bone forms the most caudal portion of the cranium, 

 entering into the formation of its caudal wall and of its base. It 

 connects the cranium with the vertebral column and surrounds 

 a large opening, the foramen magnum (d], by means of which 

 the cranial cavity communicates with the vertebral canal. 



a 



FIG. 17. OCCIPITAL BONE, CAUDAL FIG. 18. OCCIPITAL BONE, INNER 



OR OUTER SURFACE. SURFACE. 



a, basilar portion; b, lateral portions; c, squamous portion; d, foramen mag- 

 num; e, occipital condyles; f, jugular processes; g, jugular notch; A, lambdoidal 

 ridge; i, external occipital crest; /, external occipital protuberance. 



In young kittens four portions may be distinguished in this 

 bone. These are, a basal portion (the basioccipital bone), 

 two lateral portions (the exoccipital bones), and a dorsal por- 

 tion (the supraoccipital bone). These four bones remain 

 separate through life in many lower vertebrates. In the adult 

 cat they are completely united into a single bone, but it is 

 convenient to describe this bone as made up of four parts : a 

 basal portion (a) (pars basilare), corresponding to the basi- 

 occipital, two lateral portions (b] (partes laterales), corre- 

 sponding to the exoccipitals, and a squamous portion (r) 

 squama occipitalis) corresponding to the supraoccipital. 



