222 ANATOMY OF VERTEBRATES. 



moved in the direction of ' retraction,' as the limbs hang in fig. 140, 

 the ' flexors ' of the fingers have their homotypes in the hind limb 

 called 'flexors of the toes,' and the muscles effecting the opposite 

 movements of the digits are termed 'extensors' in both fore and 

 hind limbs. The muscle, 40, arising from the fascia of the knee, 

 becomes by its insertion the extensor longus digitorum pedis. 

 The mnscle, 41, is the flexor longus digitorum pedis. A short 

 extensor arises from the fore part of the tarsus ; its tendons 

 unite with those of the long extensor. A short flexor from the 

 opposite side of the tarsus divides, to be inserted by fleshy fibres 

 into the tendons of the flexor longus. The hallux has a special 

 extensor and abductor : the fifth toe has also an abductor : these 

 combining- in action, enlarge the breadth of the foot. 



In the higher reptiles, of the order Crocodilia, chiefly affecting 

 the watery element, and with frame and limbs proportioned 

 for natation, the primitive segmental structure continues to 

 be shown by the vertical aponeuroses passing outward from each 

 successive vertebra, especially from the di- and pleur-apophyses ; 

 they divide the mass of muscles answering to the caudal myo- 

 commas of Fishes and fish-like Batrachia in the tail; to the 

 spinalis dorsi, longissimus dorsi, and sacrolumbalis of higher Ver- 

 tebrates in the back ; and to the cervicalis ascendens, splenius cajntis, 

 and transversalis colli in the neck. The posterior attachment of 

 the sacrolumbalis is to the fore part of the ilium by a slender ten- 

 don : that of the longissimus dorsi is to the sacral ribs. External 

 to the longissimus dorsi is the trachelomastoideus, originating 

 behind from the diapophyses of the second or third dorsal vertebra, 

 passing forward between the di- and zyg-apophyses of the cer- 

 vical vertebrae, deriving slips therefrom, and inserted into the 

 mastoid. The complexus rises from the sides of the neural spines 

 of the middle cervical vertebras, and is inserted into the parocci- 

 pital. The splenius cajntis arises from the neural spines of the 

 anterior dorsals, and is partly a continuation of the spinalis dorsi : 

 it is inserted into the superoccipital, and shows traces of the seg- 

 mental structure. The powei'ful muscles of the tail are more 

 decidedly divided by aponeurotic septa into segments, correspond- 

 ing with the vertebra? ; but they are grouped together, by Cuvier, 

 into three pairs of longitudinal muscles. The first is neural in 

 position, and chiefly a backward prolongation of the spinalis dorsi ; 

 the myocommal septa form an angle directed forward. The 

 second is lateral, and begins by a strong tendon from the upper and 

 back part of the ilium, and by a second tendon from the ischium : 

 it is also connected with fleshy flattened fasciculi from the pubis 



