42 DISSECTION OF THE ANTERIOE LIMB. 



semilunar anastomosis. From this intra-osseous arch a great number ot 

 branches proceed. An ascending (anterior laminal) set of these leave 

 the OS pedis by the numerous small foramina which cribble its laminal 

 surface. A descending {inferior communicating) set escape from the 

 bone 1)3' the series of larger foramina which open on the sharp edge 

 separating its laminal and plantar surfaces. These inferior communi- 

 cating arteries anastomose right and left with each other^ and thus form 

 the circumflex artery of the toe. From the concavity of this artery 

 branches pass backwards, and supply the tissue of the sole. 



The Veins of the Foot. — Intra-osseous vessels. Within the os pedis 

 the arterial branches are accompanied by satellite veins. There is 

 thus a semilunar venous anastomosis, to which small veins converge 

 from the laminal surface of the bone. The blood from this sinus is 

 drained away by a larger vessel which passes out by the plantar fora- 

 men in company with the plantar artery, and joins the posterior part of 

 the coronary plexus. Eoctra-osseous vessels. The foot is richly provided 

 with a superficial system of vessels, which are arranged in the form of a 

 close-meshed network having little or no communication with the deep 

 set. This venous envelope of the foot is divided into a solar, a laminal 

 (podophyllous), and a • coronary plexus. Where the solar and laminal 

 plexuses meet, a composite venous vessel runs in company with >the 

 circumflex artery of the toe. These two plexuses communicate freely 

 with each other, and with the coronary plexus. This last consists of a 

 central part, which underlies the coronary cushion, and of two lateral 

 parts, which on each side ramify on both surfaces of the lateral cartilage. 

 By the convergence of branches belonging to this cartilaginous division 

 of the coronary plexus, the digital veins are formed ; and these drain 

 away the blood from both the intra-osseous and extra-osseous systems 

 of vessels. 



Directions. — The terminal portion of the deep flexor tendon, and the 

 synovial apparatus developed in connection with it, should now be 

 examined. 



The Deep Flexor tendon (Plates 10 and 11), when it reaches the 

 upper border of the navicular bone, widens out to form what is called the 

 plantar aponeurosis. This plantar aponeurosis plays over the navicular 

 bone by means of the navicular sheath, and is covered posteriorly by a 

 fibrous layer which ultimately blends with it. It becomes inserted into 

 the semilunar crest of the os pedis, and into the bone behind that crest. 

 The above-mentioned fibrous layer was first described by Bouley, and 

 designated by him the reinforcing slieath of the perforans. This expansion 

 is attached on each side by a slip tQ the lower half of the first phalanx, 

 and it serves to maintain the plantar aponeurosis against the navicular 

 bone. 



The Navicular or Small Sesamoid Sheath (Plate 10, fig. 2). This is a 



