MAMMALIA. 271 



the follicle near its mouth, and with it are also connected bands 

 of unstriated muscle, by contraction of which the hair can be 

 erected. The hairs are continually being shed, and are replaced 

 by new ones developed on papillae connected with the old hair- 

 follicles. 



The mammary and perineal glands are made up of tubules, 

 dilated at their ends, and lined by granular epithelium continuous 

 with the epidermis. 



The dermis is rich in blood-vessels, lymphatics, and nerves, arid 

 many nerve-fibres end in elongated ovoid touch-corpuscles. One of 

 these is closely connected with the base of each vibrissa. 



3. The endoskeleton (Figs. 84 and 85) is made up of the usual 

 histological elements. The bones are much more compact than 

 those of the pigeon, and the shafts of the long bones contain 

 marrow.* As in other cases a distinction can be drawn between 

 axial and append icular skeletons, belonging respectively to trunk 

 and limbs. 



(1) The axial endoskeleton consists of skull, vertebral column, 

 ribs, and sternum. 



(a) Skull. As in the pigeon, the mature skull is mostly com- 

 posed of bones, but these are comparatively little fused together, 

 many of the boundaries remaining apparent, even in old animals. 

 They are united, in many cases, by finely jagged edges, which 

 interlock. Such unions are called sutures. 



A small posterior cranial portion may be distinguished from a 

 much larger facial portion, the boundary between the two being 

 indicated by the large orbits. 



It is convenient to consider the cranium or brain-case which 

 constitutes most of the cranial region of the skull, as being made 

 up of three rings (not segments), named from behind forwards 

 occipital, parietal, and frontal. These rings fit closely together, 

 ventrally and dorsally, but certain gaps are left laterally. Each 

 possesses an unpaired ventral element, and the floor of the brain- 

 case is largely formed by these ventral elements, the line along 

 which they are arranged being known as the basi-cmnial axis. 



* 1. Cartilage bones: Ex-, supra-, and basi-occipitals ; basi-, pre-, and 

 orbito-sphenolds ; mesethmoid, periotic, malleus, incus, os orbiculare, stapes, 

 turbinals, palatine, pterygoid, hyoids, Vertebrae, Riba, Sternum, Appendicular 

 endoskeleton (except clavicle). 2. Membrane bones: Interparietal, parietal 

 frontal, squamosal, tympanic, vomer, lachrymal, nasal, premaxilla, maxilla, 

 jugal, mandible, Clavicle. 



