134 MORPHOLOGICAL TYPES 



eyebrows, lips, and external ears (platysma muscles) (see 

 p. 278). 



The skin in mammals is well supplied with glands of 

 epidermal origin, and of which there are three kinds : sudori- 

 parous, sebaceous, and mammary. The sudoriparous or 

 sweat-glands, are small tubes which sink into the dermis from 

 the surface, and end blindly after a certain number of coilings. 

 They serve to excrete water which is obtained from the neigh- 

 bouring blood-vessels, and in so doing they play an important 

 part in the regulation of the temperature of the body. The 

 water excreted is ordinarily converted into vapour, and thereby 

 absorbs the latent heat required for this conversion from the 

 body. 



The sebaceous glands differ from the sweat-glands in that 

 they branch repeatedly, and that their secretion is not an 

 extracellular and liquid, but intracellular greasy substances 

 which are pushed out in the loaded cells themselves. These 

 glands are usually found opening into the hair-follicles, whence 

 the greasy secretion spreads over the hair. Other glands of 

 this type open to the surface along the edge of the eyelids 

 (Meibomian glands), and into depressions at the sides of the 

 anus (perineal glands). The secretion of the latter is 

 responsible for the smell of the rabbit. 



Mammary glands or milk glands, are also characteristic of 

 the whole order Mammalia. They occur in both sexes, but 

 are normally functional only in the female. They are branched 

 tubes lying between the skin and the underlying muscles on 

 the ventral surface of the body, and opening to the surface by 

 nipples, of which there are in the rabbit about four pairs, 

 corresponding to the usual number of young born in a litter. 



The eyes have upper and lower eyelids and a small nicti- 

 tating membrane. A noteworthy feature is the presence of 

 external ears, or pinnae, which assist the sense of hearing, by 

 concentrating the waves of sound. 



The anus is at the root of the tail, and is separate from the 

 urinogenital aperture, which is situated in front of it, and takes 

 the form of a penis in the male or a vulva in the female. At 

 the sides of the penis in adult males are the scrotal sacs which 



