4 MAMMALIA. 



nate very much over the medullary, while in the Antilopes, Musk- 

 deer, arid Goats, among the Ruminantia, the very large celled me- 

 dullary substance is developed almost to the exclusion of the corti- 

 cal part. The greatest and most remarkable peculiarities both of 

 the whole internal and external structure occur in the Edentata, as 

 has been already mentioned, e. g. in Bradypus didactylus. In Myr- 

 mecophaga jubata we find very greatly elongated cortical cells, and 

 the epithelial layer of an exceedingly compact texture. In the Or- 

 mthorynchus, the spiny hairs have a broad rudder-shaped end ; they 

 are somewhat serrated, inferiorly near to the bulb, but at the apex 

 quite entire. Still more remarkable are the fir-cone shaped scales 

 of the Pangolin, and the coat of mail of the Armadillo. Here 

 indeed true tegumentary bones occur, as in the Chelonia and many 

 Fishes. 



The cetacea are an exception to the rest of the Mammalia as 

 regards their outer coverings, since their skin is destitute of hair ; 

 yet in the Whales there are short bristles growing from the in- 

 tegument of the upper and lower lip. The epidermis and its 

 lower layers (Malpighian rete) are very thick, and provided with 

 numerous pigmentary cells. The corium consists of layers of white, 

 tough fibres, which form a network having a large quantity of fat 

 interposed between them, while the fatty tissue in the interior of the 

 body, as around the kidneys, where it is very much developed 

 in other animals, is wanting. The papillary bodies are greatly de- 

 veloped. 



Sudoriparous glands occur in the integument of many animals, 

 though they have been hitherto most closely investigated in the do- 

 mestic kinds. They are everywhere distributed in the integument 

 of the Horse, which perspires profusely and from every part ; they 

 are generally largest in the skin of the sexual organs. They are no 

 less numerous, though much smaller, in horned cattle ; more con- 

 spicuous in the Sheep and Pig. The small sudoriparous glands of 

 the Dog and Cat are with difficulty detected ; it is only in the skin 

 of the nose, and especially in that of the elastic foot-pads, that they 

 are manifestly larger. 



