COMPARATIVE ANATOMY 13 



1. The maiiubrium or presternum, the arrow-shaped anterior 



piece. 



2. The mesosternum, made up of six sternebrae. 



3. The xiphisternum (xiphos, sword) or metasternum, the 

 long posterior piece. It ends in a fan-shaped xiphoid cartilage, 

 which becomes much shriveled on dry skeletons. 



Ribs of the Cat 

 A typical rib, the fifth or sixth, should be studied. It con- 

 sists of the following parts: 



1. A head or capitulum, the end of which articulates with the 

 centra of two thoracic vertebrae at the costal demifacets. 



2. A tubercule or tuberculum, a slight projection close to the 

 head, for articulation with the transverse process. 



3. The 7ieck, the short portion between head and tubercle. 



4. The shaft, the long portion between the tubercle and the 

 costal cartilage. The point of sudden turn in this portion is the 

 angle. 



5. The costal cartilage, the cartilaginous connection between 

 the ventral end of the shaft and the sternum. 



Various mammals have from nine to twenty pairs of ribs. 

 Distinguish differences between the various pairs in the cat. 

 Those ribs that connect by their own cartilages to the sternum 

 are known as true ribs, the rest as false ribs. There are normally 

 nine pairs of true and four pairs of false ribs in the cat. The 

 first three pairs of false ribs have cartilages uniting with the 

 cartilages of the last true ribs. The last pair of ribs have no 

 such cartilages and are known a.s floating ribs. 



SKULL 



Skulls occur only in vertebrate animals. In the simpler 

 species it is convenient to consider the skull as consisting of 

 two parts: (i) cranium (neurocranium) which surrounds and 

 protects the brain, and (2) visceral skeleton {splanchnocranium) 

 which forms the jaws and gill arches where these are present. 

 In higher vertebrates parts of the visceral skeleton are trans- 

 formed to serve other purposes. 



Cranium of the Shark 



On a mounted skeleton identify the cranium and visceral 

 skeleton. Observe that the visceral skeleton is not a part of 



