X BODY-WALL AND CCFXOME 489 



and neck is covered by a thin cutaneous muscle, by means of 

 which the rabbit is able to twitch its skin. Internally to 

 this muscle in the female are the mammary glands (p. 467), 

 which, when secreting, appear as long, whitish, branched 

 masses, the ducts of which can be traced to the teats, on 

 the apices of which they open by numerous small apertures. 



A whitish band of connective tissue passes along the mitl-ventral line 

 nf the abdomen from the xiphisternum to the pubis : this separates two 

 longitudinal hands of muscle, the recti abdominis, from one another ; 

 and laterally to I hem, the abdominal wall consists of three thin layers 

 of muscle with their fibres running in different directions — the external 

 oblique, the internal oblique, and the Iransversalis, the latter being 

 lined on its inner surface by Wxe peritoneum. A fibrous cord, known as 

 Poiiparfs ligament, beneath which the blood-vessels and nerves pass 

 outwards to the leg, extends upwards and forwards from each pubis 

 to the anterior part of the corresponding ilium. In the thorax the 

 muscles of the body-wall are broken up into separate portions by the 

 ribs, and thus form a series of dntercostal muscles, which are, like the 

 oblique muscles of the abdomen, arranged in two layers, external and 

 internal, and are important in respiration. 



Extending from the thorax to the fore-limb of either side 

 are the large pectoral muscles ; and a number of other muscles 

 can be seen in the neck, in the ventral middle line of which, 

 covered by the cutaneous muscle, the windpipe or trachea is 

 visible. The trachea is strengthened by a series of carti- 

 laginous rings, and ends in front in the larynx, situated 

 between the two rami of the mandible ; and just in 

 front of the larynx is the hyoid bone (p. 479), embedded 

 in a' mass of muscle. 



The Coelome and its contents. — On cutting open the 

 body-cavity, it will be seen to be divided into two main 

 chambers — the thoracic and abdominal cavities — by means of 

 the diaphragm (Fig. 125, d). The relatively small thorax — 

 which is lined by a serous membrane corresponding to the 



