256 ZOOLOGY SECT. 



between the transverse processes, partly between the ilia and the 

 urostyle. The ventral muscles are differentiated into a paired 

 median band, the rcctus abdominis (Fig. 875, ret. abd) with longi- 

 tudinal fibres, and a double layer of oblique fibres obliquus 

 externus (obi. ext) and internus (obi. int) - - extending from the 

 vertebral column to the recti. Both the extensor dorsi and the 

 rectus abdominis are traversed at intervals by transverse bands 

 of fibrous tissue, the inscriptions tendinece (ins. ten), but the 

 segments thus formed do not correspond with the embryonic 

 myomeres. The right and left recti are united by a longitudinal 

 band of tendon, the linea alba (I. alb). 



The muscles of the limbs are numerous and complex, each seg- 

 ment having its own set of muscles by which the various move- 

 ments of which it is capable are performed. There are muscles 

 passing from the trunk to the limb-girdles ; from the trunk or the 

 limb-girdles to the humerus and femur ; from the humerus and 

 femur to the radio-ulna and tibio-fibula ; from the fore-arm or 

 shank to the digits ; and from one segment of a digit to another. 

 For the most part the limb-muscles are elongated and more or less 

 spindle-shaped, presenting a muscular portion or belly which passes 

 at either end into a tendon of strong fibrous tissue serving to fix 

 the muscle to the bones upon which it acts. The relatively fixed 

 end of a muscle is called its origin, the relatively movable end its 

 insertion, e.g. in the gastrocnemius muscle of the calf of the leg (gstr) 

 the proximal end attached to the femur is the origin, the distal 

 end attached to the foot the insertion. According to their action 

 muscles are divided into flexors which bend, and extensors which 

 straighten one part upon another; adductors which draw towards, 

 and abductors which draw away from, the middle line ; elevators 

 which raise and depressors which lower a part, such as the lower 

 jaw. The names of the muscles may have reference to their 

 position, e.g. pectoralis(pct.), the principal muscle of the chest ; or to 

 their form, e.g. bice}},?, the two-headed muscle ; or to their action, 

 e.g. flexor tarsi; or to their origin and insertion, e.g. coru.co- 

 humeralis. 



Digestive Organs.- -The mouth leads into a wide buccal 

 cavity having in its roof the posterior narcs (Fig. 876, p. na.), 

 a pair of projections due to the downward bulging of the large 

 eyes, and the openings of the Eustacliictn tubes (eus. t, vide infra). 

 On its floor is the large tongue (tng), attached in front and free 

 behind, where it ends in a double point ; by means of its muscles 

 it can be suddenly projected, point foremost, from the mouth, and 

 is used in the capture of Insects. Immediately behind the tongue 

 is the glottis (gl). Teeth are arranged in a single series round the 

 edge of the upper jaw, attached to the premaxillse and maxilla? ; 

 there is also a small patch of teeth (vo. t) on each vomer just 

 internal to the posterior nostril. The teeth are small conical 



