CLASS MAMMALIA 637 



clavicles, and two knob-like coracoids. Each half of the pelvic 

 girdle is called an innominate bone, and is made up of the ilium, 

 ischium, and pubis fused together. The concavity in the in- 

 nominate bone in which the head of the femur articulates is 

 called the acetabulum. 



The ankle-joint of the rabbit lies between the tibia and fibula 

 above, and the tarsal bones below. The fourth and fifth carpal 

 bones and corresponding tarsal bones are fused together, forming, 

 in the fore limb, the unciform bone, and in the hind limb the 

 cuboid bone. One of the sesamoid bones of the hind limb which 

 is situated on the front of the distal end of the femur is called 

 the kneepan, or patella. The tibiale is fused with the inter- 

 medium of the tarsus to form the astragalus; and the fibular e, 

 which lies along its outer side, is called the calcaneum. 



Internal Anatomy. — Unlike other vertebrates, the body- 

 cavity of the rabbit and mammals in general is divided by a 

 transverse muscular partition, called the diaphragm, into two 

 parts, an anterior thoracic portion containing the heart and 

 lungs, and a posterior portion containing the abdominal viscera. 



The Digestive System. — The mouth or buccal cavity bean* 

 on the anterior portion of the roof a series of transverse ridges 

 against which the tongue works. That part of the roof which 

 has a bone foundation is known as the hard palate. Posterior 

 to this is a muscular flap, the soft palate, which separates the 

 mouth from the pharynx. At the sides of the posterior part of 

 the soft palate are a pair of small masses of lymphoid tissue 

 containing pits of unknown function, called the tonsils. The 

 tongue is attached to the floor of the mouth. It bears a number 

 of taste papilla on the anterior part and sides. The two orifices 

 of the eustachian tubes and the two apertures of the nasopalatine 

 canals, which connect the nasal and buccal cavities, are situated 

 in the roof of the mouth behind and above the soft palate. There 

 are four pairs of salivary glands: (1) the parotids, (2) the infra- 

 orbitals, (3) the submaxillaries, and (4) the sublinguals. They 

 pour their secretions into the mouth cavity. 



