LEPUS CUNICULUS 273 



they are particularly well developed and exhibit a characteristic 

 structure : such sensory hairs also possess a series of venous sinuses 

 at their bases. 



Primitively connected with the hair follicle of the mammal are 

 two sets of glands, the sweat and the sebaceous glands. The latter 

 are small saccular glands lined by a secretory epithelium composed of 

 characteristic large .cells. They arise singly or in pairs about half- 

 way down the follicle. The cells secrete a fatty substance and then 

 themselves disintegrate in order to produce the characteristic 

 sebaceous secretion. The sweat glands are developed from higher 

 up the follicle, and may later lose connection with it altogether. 

 When fully formed, they consist of a long corkscrew-like duct 

 passing deep down into the dermis to terminate in a fairly closely 

 coiled secretory tubule. The secretory portion is lined by a cubical 

 epithelium, and the sweat is produced in the cells and passed out into 

 the lumen. In man these glands are developed all over the general 

 surface of the body, and are particularly numerous on the palms of 

 the hand, but in the rabbit they are restricted to certain limited 

 areas. 



The mammary glands are highly modified sweat glands pro- 

 ducing their secretion, the milk, in a similar manner, and they are 

 developed in connection with special groups of hairs along the 

 axillary-inguinal line. 



The muscular system of the rabbit calls for little special 

 notice, since it is not intended to enter into a detailed description of 

 the individual muscles. It is divisible, as in the frog, into voluntary 

 or striate muscles and involuntary or non-striate muscles, and also 

 the heart is composed of characteristic cardiac muscle. The whole 

 of the ventral and lateral regions of the trunk and the neck have 

 a thin layer of cutaneous muscle attached closely to the inner side 

 of the skin, and so enabling the animal to twitch its skin quite 

 independently of the underlying body wall. Recti Abdomnis and 

 oblique muscles essentially similar to those in Rana are found in the 

 abdominal region ; but inside the oblique is a further thin muscular 

 layer, the transversalis covered by the peritoneum. In the thoracic 

 region, however, this arrangement is broken up by the ribs, and we 

 find it replaced by a series of internal and external intercostal 

 muscles which play an important part in respiration. Yet one 

 further structure deserves attention, and that is the diaphragm. 

 This is a thin arched sheet with a tendinous centre into which are 

 inserted radial muscles originating in the ribs and on the vertebral 

 column, and it completely separates thoracic and abdominal 

 cavities. Two particularly strong bands known as the pillars of 

 the diaphragm pass dorsally one to each side of the vertebral 



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