406 THE PIGEON. PHYLUM CHORDATA 



with the sacrum along nearly the whole of its inner side to form 

 a single structure, the synsacrum. This long bone enables the 

 trunk to be supported in a more or less horizontal position by 

 the single pair of legs. The acetabuhim is placed near the middle 

 of the ilium. The ischium is a flat, backwardly directed bone. Its 

 hinder part is fused with the ilium, but just behind the acetabulum 

 an oval opening — the iliosciatic foramen — lies between the two. 

 The pubis is slender and also directed backwards. In many birds 

 it has a small prepubic or pectineal process in front. The obturator 

 foramen is slit-like. There is no symphysis or ventral junction 

 of the girdles. The hind-limb has a short, stout femur, and below 

 this is a long tibiotarsus, made up of the tibia and the proximal 

 tarsals. The slender fibula is free above but fused with the tibio- 

 tarsus below. The distal tarsals are fused with metatarsals 2 to 4 

 to form a single tarsometatarsus, which has a characteristic 

 trifid end. The first metatarsal is free, and there are four digits, 

 with phalangeal formula 23450. 



MUSCULAR ARRANGEMENTS 



The most conspicuous part of the muscular system is the great 

 pectoral muscles. The pectoralis major, arising from the sternum 

 and clavicle, is inserted on the under side of the humerus, which 

 it pulls downwards. The smaller pectoralis minor arises from the 

 sternum above the major and passes through the foramen 

 triosseum and over the shoulder to its insertion on the upper side 

 of the humerus, which it raises. The perching mechanism is also 

 interesting. The flexor tendons which curve the toes round a 

 branch are so arranged that they are tightened by the bending 

 of the metatarsus on the tibia in perching, so that the bird does 

 not fall even when it is asleep. 



ALIMENTARY SYSTEM 



The mouth has no teeth or true palate (false roof, p. 438), 

 but there are large posterior nares partly hidden by soft palatal 

 folds, a single opening for the Eustachian tubes, and a sharp- 

 pointed tongue. The glottis is not protected by an epiglottis as 

 in the rabbit. The gullet widens into a thin-walled crop (Fig. 321), 

 in which the food is stored. From the crop the gullet continues 

 to the stomach, which has two parts, first the fore-stomach 



