Fig. 94. Tendon Sheaths on the Dorsal Aspect of the Right Hand. 



Skin, Superficial Fascia, Vessels, except the Radial Artery, and Nerves have 

 been removed. The Posterior Annular Ligament is intact, but supposed to be 



transparent. 



The tendon or synovial sheaths of the Extensor Tendons lie in special 

 compartments between the Periostium of the bones of the forearm and the wrists 

 on one hand, and the Posterior Annular Ligament on the other hand; they 

 extend upwards as far as this ligament, i. e. as far as transverse fibres are present ; 

 below, they extend 1^1^/4 inch beyond the ligament. 



The synovial sheaths may, however, extend higher (^/r.ths inch or more 

 above the highest transverse fibres, vide infra). 



Starting at the outer (radial) side, and going inwards, we find 6 Com- 

 partments and Sheaths for the Tendons of the following muscles: 



1. Extensor Ossis Metacarpi Pollicis, and Extensor Primi Internodii; the 

 sheath for the latter muscle is about y.^ inch longer than the sheath for the former. 



2. Extensor Carpi Radialis Longior, and Extensor Carpi Radialis Brevior. 



3. Extensor Secundi Internodii. The latter crosses the Radial E.x. tensors 

 at an acute angle, lying on them, i. e. posterior to them. These three sheaths 

 usually communicate, and are to be considered as forming practicall)' one sheath. 



4. Extensor Communis Digitorum and Extensor Indicis. The two tendons 

 for the index finger lie in one sheath which communicates with the common 

 sheath for the 3rd, 4th and 5th fingers. The index sheath is, however, shorter. 



5. Extensor Minimi Digiti. The sheath of this muscle, which sometimes 

 has two tendons (cf. figure) is usually longer than the others mentioned above. 



6. Extensor Carpi Ulnaris, this sheath is quite short, because the muscle 

 ends at the base of the 5th Metacarpal Bone. 



The broad tendinous slips which connect the tendons to the 2nd, 3rd and 

 4th fingers are remarkable. Morphologically, they probably represent the form- 

 ation of one broad aponeurosis, analogous to the one on the palmar aspect 

 which is fully developed. 



Subcutaneous Bursae are shewn (cf. figure) on the 2nd and 3rd fingers. 

 They are due to continuous pressure (professional bursae). 



The Tendon Sheaths accompany the movements of their tendons. The 

 distal ends of those sheaths which belong to tendons inserted into the metacarpal 

 bones, are easily determined. In order to find the distal ends of the others, the 

 fingers should be completely flexed and hardened with injections of Eormalin. 



The proximal ends were determined, from another specimen, in the dorsi- 

 flexed position with extended fingers (cf. the black and red lines above the 

 posterior annular ligament). 



The length of the Tendon Sheaths varies according to the size of the 

 hand. Those of the Extensors of the Carpus are the shortest and of about equal 

 length (Vi5~Vi5 inch). The sheath of the Extensor Communis Digitorum which 

 often contains several compartments, varies most (3^5 — 3-/5 inches). It is some- 

 times longer in small hands than in large ones. The weakest tendons have the 

 largest sheaths. Extensor Secundi Internodii, Extensor Primi Internodii, and 

 Extensor Minimi Digiti; their respective lengths are: 2Y5 — 2%; 2^5 — 2V5; 2^1^ — 3Vf, 

 inches. 



