EXTREMITY. 



169 



where the crucial ligaments are attached. 

 Anterior and posterior to this spine are two 

 rough depressions, the posterior more hollowed 

 than the anterior : into the former the posterior 

 crucial ligament is inserted, and the latter re- 

 ceives the anterior crucial ligament. 



The circumference of the head is rough and 

 perforated by a vast number of minute vas- 

 cular foramina. Each condyle projects late- 

 rally beyond the plane of the corresponding 

 surface of the shaft, the internal to a greater 

 extent than the external. These lateral pro- 

 jections are distinguished by the name of Tu- 

 berosities. The internal tuberosity gives in- 

 sertion at its lower part to the internal lateral 

 ligament of the knee-joint; posteriorly this 

 tuberosity is grooved, and one of the tendons 

 of the semi-membranosus is inserted into the 

 groove, and separates the internal lateral ligament 

 from the bone in this situation. At the pos- 

 terior part of the external tuberosity there is a 

 small articular facet, nearly circular and plane, 

 with which the fibula is articulated. 



In front of the head of the tibia there is a 

 rough triangular surface, the apex of which 

 is directed downwards and forms a promi- 

 nence, which is smooth at its superior part, but 

 rough inferiorly. The ligamentum patellae is 

 inserted in the latter situation; the smooth 

 portion indicates the position of a bursa which 

 intervenes between the ligament and the bone. 

 This prominence is called the anterior tube- 

 rosity, and by some anatomists the spine. 

 From the inferior rough portion of this tube- 

 rosity there passes upwards and outwards a 

 prominent line, most prominent at its ter- 

 mination, where the tibialis anticus muscle has 

 one of its attachments. 



The shaft of the tibia has the form of a 

 triangular prism in almost its whole extent: 

 at its inferior third this form is less distinct, 

 in consequence of the angles being rounded off. 

 Of the three surfaces the anterior is that which 

 presents the greatest dimensions : it is smooth 

 and slightly convex in its entire extent, in- 

 clined backwards and inwards, subcutaneous, 

 except at its upper part, where an aponeurotic 

 expansion connected with the tendons of the 

 semi-tendinosus, sartorius, and gracilis muscles. 

 The inferior fourth of this surface is much 

 more convex than the upper portion, and looks 

 directly inwards. The external surface is in- 

 clined backwards and outwards, and is con- 

 cave in its three superior fifths, convex in the 

 rest of its extent. The depth of the superior 

 concave portion is proportionate to the de- 

 velopement of the tibialis anticus muscle, to 

 which it gives insertion. The inferior con- 

 vex portion is of less extent than the superior, 

 and as it descends it experiences a change of 

 aspect so as to look directly forwards. This 

 change is in accordance with the altered di- 

 rection of the tendons of the tibialis anticus 

 and extensor muscles of the toes, which lie in 

 contact with the bone in this situation. The 

 posterior surface is expanded at its extremities 

 and contracted in the centre. At its superior 

 part a triangular surface is marked off from 

 the rest, towards the upper extremity by an 



oblique line, which proceeds from below up- 

 wards, and from within outwards; into this 

 line are inserted the poplitseus, soloeus, tibialis 

 posticus, and the long flexor muscle of the 

 toes. The space which intervenes between 

 this line and the posterior margin of the head 

 of the bone is covered by the poplitaeus muscle 

 and forms part of the floor of the popliteal 

 space. Immediately below this oblique line, 

 the orifice of the nutritious canal is situated, 

 penetrating the bone obliquely downwards; 

 this canal is the largest of the medullary canals 

 of the long bones ; and Cruveilhier states that 

 he has traced a nervous filament passing into 

 it in company with its artery. All that portion 

 of the posterior surface which is below the 

 oblique line is smooth and divided by a ver- 

 tical line, which is variously developed in dif- 

 ferent subjects; the tibialis posticus muscle 

 and the long flexor of the toes are attached to 

 this surface. 



Three distinct edges separate these surfaces. 

 The anterior edge (crista tibia) is very promi- 

 nent and sharp in its three superior fourths, but 

 rounded off' below : in its upper part it is quite 

 subcutaneous, and may be felt under the skin. 

 The external edge forms a very distinct line of 

 demarcation between the internal and posterior 

 surfaces ; it gives attachment to the interosseous 

 ligament, and at its inferior extremity it bifur- 

 cates and encloses a concave triangular surface, 

 in which the fibula rests. The internal edge is 

 more rounded than either of the others ; more 

 distinct inferiorly than superiorly. At its up- 

 per end it gives insertion to the internal lateral 

 ligament of the knee-joint and the popliteus 

 muscle, and lower down to the solceus and the 

 common flexor of the toes. 



The inferior or tarsal extremity of the tibia 

 is of larger dimensions than the shaft, although 

 much smaller than the superior. On its infe- 

 rior surface we notice a quadrilateral articular 

 cavity, of greater dimensions transversely than 

 from before backwards, concave in this latter 

 direction, and slightly convex transversely, in 

 consequence of the existence of a slight ridge in 

 the centre, which passes from before backwards. 

 This surface is for articulation with the supe- 

 rior part of the body of the astragalus to form 

 the ankle-joint. 



The anterior surface of the inferior extremity 

 of the tibia is convex and rough ; it gives in- 

 sertion to the anterior ligamentous fibres of the 

 ankle-joint, and the tendons of the extensor 

 muscles pass over it. The posterior surface is 

 very slightly convex ; sometimes a very super- 

 ficial groove exists upon it for lodging the ten- 

 don of the flexor pollicis longus ; and internal 

 to that, and lying behind the internal malleolus, 

 a more distinct and constant groove, which 

 passes obliquely downwards and inwards, and 

 lodges the tendons of the tibialis posticus and 

 flexor communis. 



On the inside of the inferior extremity, we 

 observe that the bone is prolonged downwards 

 and slightly inwards, forming a thick and flat- 

 tened process, quadrilateral in form, called 

 malleolus internus. The internal surface of 

 this process is rough and convex; it is quite 



