578 CHORDATA. 
but these gradually arise as small protuberances covered with hair or 
“velvet.” When the antlers are full-grown the ‘‘ velvet” isrubbed off 
by the deer by friction against trees or other objects until the bony 
antler alone remains. The branches of the antler are called ‘‘ tynes,” 
and in those species with many tynes the number of these increases every 
year. Antlers are usually confined to the male sex. 
The musk-deer (A/oschus) and the water-deer (Hydropotes) have no 
antlers in either sex, but, on the other hand, they retain the upper canine 
teeth as long sharp tusks. ' 
In all the Pecora the placenta is cotyledonary, a specialised derivative 
of the diffuse. 
The true deer are not found in the Ethiopian region, their place 
being taken by the ‘“‘horned” antelopes. To this region are confined 
the giraffes. The sheep, oxen and goats are more or less northern 
forms, the north temperate regions of Eurasia and N. America being 
their headquarters. 
The above five families of Artiodactyla are intimately 
connected by numerous fossil forms. 
ORDER XI.—Cefacea. 
The porpoise has been described as a typical aquatic 
mammal and it also serves as a type of the order Cezacea. 
Under the heading of the porpoise we have noticed the 
adaptations to an aquatic life which constitute the main 
peculiarities of the Cefacea. These consist of the follow- 
ing :— 
1. Fish-like shape, with dorso-ventral coloration. 
2. Loss of hair and external ears and formation of 
“ blubber.” 
3. Fore-limbs formed into fins, hind-limbs lost and tail 
forming a fin. 
4. Homodont dentition (fish diet). 
5. Modification of nostrils to form vertical blow-hole and 
prolongation of larynx. 
6. Retia mirabilia. 
4. Loss of salivary and lacrymal glands. 
In addition, we may note the well-convoluted cerebrum 
of the brain and the abdominal testes. The stomach is 
usually somewhat complex, though the whole order is essen- 
tially carnivorous—an important distinction from the Sivenia. 
The uterus is bicornuate and the placenta, like that of many 
Ungulata, is diffuse and non-deciduate. 
