


Rs eine rae BULLETIN NO. ate 
box, known as the skull. Pepdent openings in ine duane thes? sa 
nerves passing from the brain to the organs of sense i ed. 
When the spinal column is ossified, it is divided into distinct — 
elements or vertebre. The vertebral column is the central a 
support as well as the axis of the body. Nearly all paired or- aye 
gans are symmetrically arranged on either side of it. The 
bones which constitute the framework of the body and limbs . 
are directly or indirectly attached to it. Of external movable 
limbs used in locomotion there are never more than four which 
although variable in position and function may always be recog- ~— 
nized as a posterior and anterior pair. The heart is ventral, 
that is, on the same side of the vertebree as the alimentary sys- ane 
tem. 5 ee 
_ Vertebrates are of five distinct sorts which constitute the ay 
classes Pisces (fishes), Amphibia (frogs and salamanders), — 
Reptilia (reptiles), Aves (birds), and Mammalia (mammals). 
Of these five groups the first two and the second two aremore —_— 
naturally allied with each other than with any of the other 
classes. This more intimate relationship is indicated by uniting At ee 
fishes and batrachians under the common term Jcthyopsida and 
the reptiles and birds under the name Sawropsida. (Theterms 
Branchiata and Monocondyla are of the same extension asthe 
above, but less convenient. In order to preserve uniformity in 
the number of sub-divisions, Mammals are sometimes given as ; 
the only class under the province Zygencephala co-ordinate 
with the above.) As distinguished from these groups, Mam- 
mals possess the following pecularities: 
The female has mammee or glands which secrete a milky fluid | K 7 
to sustain the young, which, after birth, pass through along — th re | 
period of comparative helplessness. The two halves of the ae A 
anterior part of the brain (cerebrum) are connected by a cor-  _ 
pus callosum. There are two condyles or articulating surfaces’ os, 
at the back of the skull. The lower jaw is composed of asingle _ a 
Ss 
bone on each side and the ear contains the malleus and incus. eR 
The heart has four chambers and a single aortic arch. The er 
diaphragm is perfect and the lungs are freely suspended in the _ < 
thoracic cavity thus formed. 4 chy 
The ribs join the sternum. There are no gills at any timein — Pes 
life. Blood is warm and the red corpuscles unnucleated. The a 
body is covered more or less completely with hair. hens 
The scientific definition cf a mammal would comprise the ~ oe 
points above mentioned and others of similar nature, but prac-— 
tically the notion which springs unbidden in our minds when the 

