363 THE ANIMAL KINGDOM. 



remain separate. It is divisible into three regions a praesternum or 

 manubrium sterni, with which the clavicles and first pair of ribs articulate ; 

 a mesosternum composed of a variable number of sternebrae with a pair 

 of ribs articulating between every two adjoining sternebrae, the last sterne- 

 bra, however, sometimes, e. g. in Man, giving attachment to more than one 

 pair of ribs ; and a xiphisternum, sometimes cartilaginous, sometimes ossi- 

 fied, representing a sternal region in which the original connection with 

 ribs has been aborted. The fore-limbs are never absent ; the hind-limbs 

 are wanting in Cetacea and Sirenia, or reduced to rudiments of a femur, 

 and in the Greenland Whale of a tibia as well. The scapula has the true 

 anterior border or spine placed on the external surface of the bone, and the 

 apparent anterior border is a new development. The coracoid is a small 

 process which forms a portion of the glenoid cavity but fails to reach the 

 sternum. The clavicle, originally continuous with the acromion or free 

 extremity of the spine, articulates with the praesternum and may either be 

 represented by ligament at each end, e. g. many Carnivora and Rodentia> or 

 be absent altogether, e. g. Ungulata, Cetacea. The interclavicle is fused 

 with the praesternum ; it may be partially converted into ligament or atro- 

 phied away completely. The ilium slopes downwards and backwards from 

 its articulation with the sacrum. The pubes meet in a ventral symphysis 

 with rare exceptions (e. g. the Mole, Talpa) ; the ischia on the contrary have 

 no symphysis, or only just touch one another. There is a well-developed 

 heel, or os calcis, formed by the growth of the fibular tarsal bone. The 

 digits are limited to three phalanges in addition to the metacarpal and 

 metatarsal bones, except in the hand of some Cetacea^ where the second 

 and third fingers have a larger number. The bones of Mammalia, with 

 the exception of those of the skull, of the sternebra, and save in a few 

 cases of the carpus and tarsus, possess epiphyses or separate caps of bone 

 to their free extremities or articulating surfaces. 



The cerebral hemispheres are the largest part of the brain : their 

 surface is often convoluted, and they are connected by a system of trans- 

 verse commissural fibres, the corpus callosum, as well as by longitudinal 

 fibres, the fornix. Their ventricles are large and form an anterior and a 

 descending cornu with the addition in the higher Primates of a posterior 

 cornu. The olfactory lobes are usually small, and are absent in toothed 

 Whales : the olfactory nerves very numerous, and perforating the ethmoid 

 bone in small bundles so as to give it a sieve-like aspect (the cribriform 

 plate). The anterior commissure is small. The pineal gland has no con- 

 nection with the dura mater or the skull ; is small, and its base alone con- 

 tains nervous substance. The optic lobes are small, solid, and divided by 

 a transverse fissure into four lobes the corpora quadragemina. The 

 lateral lobes of the cerebellum are large and connected by a pons Varolii, 

 or set of ventral transverse fibres. The angle, or bend, between the 



