542 MR. J. C. GALTON ON DASYPUS SEXCINCTUS. 



I Lenle, moreover, says, concerning these muscles in man, that the e. r. brevior is occs 

 raally absent, or has so grown together with the e. r. longior that this latter appear 



to give oil' two tendons l « 



1 tensor ossis metacarpi pollicis. — This is a muscle of great length. It arises from 

 tin? fossa included between the ridge which forms the inner boundary of the ulna and 

 another ridge which runs down from the humeral articular surface of the bone to join 

 the former, at the distance of about three quarters of an inch from the tip of the ole- 

 cranon — also from the adjoining portion of the capsule of the joint, and from the strong 

 interosseous septum between radius and ulna. 



It then runs along the radial side of the extensor indicis for some distance, taking a 

 direction obliquely towards the radial side of the carpus, and passes, also obliquely, over 

 the radius, immediately behind the " crista-galli"-like termination of the median dorsal 

 ridge of this bone, being bridged over by a thin ligamentous arch, which stretches from 

 the above-mentioned terminal crest longitudinally to the median ridge, which runs from 

 it backward. The muscle appears to derive a few accessory fibres from the radial crest, 

 and becomes tendinous immediately upon leaving the radius for the carpus. The short 

 tendon then passes under a fragile ligamentous bridge, stretching from a tubercle pro- 

 jecting from the dorsum of the scaphoid bone (?) across to the styloid process of the 

 radius, or a sesamoid in its immediate vicinity, and is finally inserted into the base of the 

 metacarpal of the pollex, on its radial side. Under that portion of the muscle which 

 lies between the terminal crest of the median radial ridge and the beginning of its proper 

 tendon, pass the two tendons of the extensor carpi radialis into the palm. Meckel 

 expressly states that this muscle is absent in the "Tatu" 2 . 



Extensor indicis.—A narrow, flat, strap-shaped muscle, of uniform breadth, arising 

 from the strong ridge which runs along the inner edge of the ulna, at the beginning of 



forearm 



the distal half of the bone. It then turns suddenly inwards towards the middle line of 



and, running on the radial side of the mesial ridge, which is developed 

 upon the distal third of the dorsum of the ulna, close to the ulnar edge of the extensor 

 ossis metacarpi pollicis, passes under the ligamentous bridge which crosses over the 

 extensor communis, on to the dorsum of the carpus. It soon becomes tendinous ; and 

 the tendon almost at once divides into two unequal portions, the larger of which, broad 

 and flat, passes to the base of the proximal phalanx of the index ; while the smaller, 

 slight and cord-like, terminates at the base of the ungual phalanx of the pollex. 

 This muscle is, for the greater part of its course in the forearm, overlapped by the 



extensor communis. 



According to Meckel, the index alone in the "Tatu" receives a tendon from this 

 muscle'. The same anatomist states that this extensor sometimes sends, but not always, 

 a small offset to the poUex in the Beaver. Its tendon, moreover, in the Bear and Coati, 



among Carmvora, passes to the pollex as well as to the index. 

 Sttentor communis digitorwm.-A moderate-sized fusiform muscle, which arises from 



the strong ndge above the external condyle of the humerus, immediately below the 



ongm of the extensor carpi radialis, with the lowermost fibres of which muscle its own 



' **>**«• P- 20 f « Of. * p. 553. 3 op. cit. p. 551. 



