MAMMALIA 271 



The bones maintain their relative position by the periosteum 

 being carried across, uniting the two ends, and this, called the 

 capsular ligament, is strengthened in regions where movement 

 is absent or restricted, for many of the joints are hinge joints. 

 The result is that special lateral ligaments are developed. 

 Additional ligaments are provided where necessary, and the 

 whole framework of the skeleton is thus intimately connected 

 by connective tissue, by special ligaments of connective tissue, 

 and by muscles. 



Ligaments may therefore be denned as connective-tissue 

 sheets or bands uniting bones together. In some cases they 

 have been derived from muscles which have degenerated. 



Muscles are invested in and are divided up by connective 

 tissue, and in the many cases where the muscle is continued 

 into a tendon the connective tissue of the latter is continuous 

 with that which invests and supports the muscle. A tendon 

 therefore is a sheet or band of connective tissue which connects 

 muscle with bone. As we have observed in other cases, the 

 connective tissue is so generally spread throughout the body, 

 connecting the bones, running from the bones to form liga- 

 ments and tendons and the sheaths of muscles, that it forms 

 a universal pathway for the blood-vessels and nerves which 

 have also to reach every part of the body. 



The skin of a mammal such as the rabbit is formed of a 

 many-layered epidermis based on a connective-tissue dermis. 

 The former is derived from the ectoderm and the latter from 

 the outer layer of the myotomes, and from mesenchyme. The 

 epidermis in section is seen to be resolved into an inner living 

 region called the Malpighian layer, and an outer stratum 

 corneum wherein the cells become flat and horny, thus forming 

 a protection to the other. The external corneal cells are 

 shed constantly, and the layer is being at the same time 

 renewed from the Malpighian layer, and it from the innermost 

 layer. The dermis, true skin, or leather part of the skin is 

 formed of connective tissue and it bears nerves and blood- 

 vessels, both of which penetrate into folds or pits which form 

 papillae at the junction between the dermis and the epidermis. 

 Fat is deposited in the internal part of the dermis. 



The function of the skin primarily is to form an elastic, 



