506 THE RABBIT CHAP. 



by means of which the rabbit is able to twitch its skin. 

 Internally to this muscle in the female are the mammary 

 glands (p. 483), which, when secreting, appear as 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 mid- 

 ventral line of the abdomen from the xiphisternum to the 

 pubis : this separates two longitudinal bands of muscle, the 

 recti abdominis, from one another ; and laterally to them, 

 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 transver satis, 

 the latter being lined on its inner surface by the peritoneum. 

 A fibrous cord, known as Poupart's ligament, beneath which 

 the blood-vessels and nerves pass outwards to the leg, 

 extends upwards and forwards from each pubis to the corre- 

 sponding 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 intercostal muscles, which, like the oblique 

 muscles of the abdomen, are 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 

 v/indpipe or trachea is visible (Fig. 135). The trachea is 

 strengthened by a series of cartilaginous 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. 496), embedded in a mass of muscle. 



The Ccelome 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. 135, d). The relatively small 

 thorax which is lined by a serous membrane corre- 

 sponding to the peritoneum of the abdomen and known 

 as the pleura contains the lungs, as well as the heart 



