ySo PHYLUM CHORDATA : CLASS MAMMALIA 



palate^ formed from premaxillce^ maxillce, and palatines, 

 separates the buccal cavity from the nasal passages. In most 

 cases there are teeth, borne in sockets by the premaxillce, 

 maxillce, and mandible. 



Except in Monotremes, the coracoid is represented by a 

 small process from the scapula, and sometimes by a small 

 ossification in the glenoid cavity. The sternum includes — 

 (a) a presternum, with which the clavicles {if well developed) 

 articulate ; (b) a mesosternum divided into segments, with 

 which the sternal parts of the ribs articulate ; and (c) a 

 xiphisternum, often cartilaginous . There are generally two 

 sacral vertebrce, but several caudals, and more rarely a 

 lumbar, may be fused to these. The ilio-sacral articulation 

 is in front of the acetabulum. The ventral symphysis is 

 usually restricted to the pubes, but in some Insectivores and 

 Bats these do not meet. Except in Echidna, the acetabulum 

 is completely ossified, and there is often a special acetabular 

 bone. The ankle joint is cruro-tarsal. 



The cerebral hemispheres have usually a convoluted surface, 

 and always cover the optic thalami and the optic lobes {now 

 fourfold corpora quadrigemina), and in higher forms the 

 cerebellum as well. The commissural system is well developed, 

 being especially represented by a large corpus callosum, except 

 in Monotremes and Marsupials, in which the anterior com- 

 missure is large and the corpus callosum absent or very small. 

 There is also an important set of longitudinal fibres called the 

 fornix. 



Characteristic of Mammals is the differentiation of an area 

 of cerebral cortex which has been called the neo-pallium- — 

 the seat of optic, auditory, tactile, and other tidings, of associa- 

 tive memory, and of attentive manipidations . From tree- 

 shrew to tarsier,from marmoset to monkey, this unifying area 

 of the brain becomes increasingly important, and the olfactory 

 region less. 



Except in Monotremes, in which there is a cloaca, the food 

 canal ends separately from the urinogenital aperture. 



The heart is four-chambered, and the temperature of the 

 blood is high, though lower than that of Birds. There is but 

 one aortic trunk, which curves over the left bronchus. The 

 red blood corpuscles are, when fully formed, non-nucleated, 

 and appear as slightly biconcave discs, circular in outline. 



