NORMAL ANATOMY OF THE KNEE-JOINT. 



45 



ment of the lateral ligaments ; below which, on 

 the outer condyle, there is a pit for the origin 

 of the popliteus tendon, and a fossa leading 

 upwards and backwards from it which lodges 

 the tendon when the joint is fully flexed. In 

 the lateral aspect of the bone we best see the 

 peculiar curvature of the articulating surface. 

 In two adult, but rather small, specimens before 

 me the inferior part of the outer condyle is a 

 segment of a circle of fourteen lines radius, 

 while the radius of the posterior portion is only 

 seven lines; similar measurements of the curves 

 of the internal condyle give radii of six and 

 twelve lines respectively : the centre of the 

 smaller circle coincides precisely with the point 

 of attachment of the lateral ligament on each 

 side, and the advantages of this arrangement 

 will appear when we come to consider the 

 functions of the joint. The smooth articulating 

 surface of the trochlea and condyles is, in the 

 recent state, covered with cartilage. Above 

 this surface and in the fossa between the con- 

 dyles are numerous foramina for the transmis- 

 sion of the nutrient vessels of the bone, the 

 internal structure of which is here made up of 

 minute cancelli. The lower extremity of the 

 os femoris is cartilaginous at birth, becomes 

 ossified from a separate centre, and long conti- 

 nues to form an epiphysis ; but ;t is ultimately 

 joined to the shaft by perfect bony union. 



The thigh-bone exposes the largest extent of 

 surface in the knee-joint; that of the tibia is 

 the next in size. Its superior extremity is ex- 

 panded into the same kind of cancellated struc- 

 ture as the os femoris possesses at its lower 

 part ; and the width from side to side equals 

 that of the condyles, which rest upon its upper 

 surface. That surface is nearly horizontal, in 

 the erect position of the body ; it is irregularly 

 oval, the long axis passing from side to side, 

 and is marked in the centre by a rough promi- 

 nence or spine, in front of which is a depression, 

 and at the back part a notch. On each side of 

 these inequalities there is a smooth articular 

 surface; the inner one the larger, especially 

 from before backwards, and slightly concave ; 

 while the outer one is flat round the margin 

 and raised at the inner side by the base of the 

 spine. Viewing the bone in its anterior aspect 

 we observe that below the articular surface it 

 slopes downwards and forwards to the tubercle 

 winch stands out at the upper part of the shin 

 or crest of the tibia; this tubercle gives insertion 

 at its lower part to the strong ligament of the 

 patella, a bursa being interposed between that 

 ligament and its upper smooth portion. Nu- 

 merous foramina are to be observed round the 

 head of the bone for the purposes of its nutri- 

 tion. Below the tubercle a section of the tibia 

 shows it much reduced in size and somewhat 

 triangular in shape ; the outer side forming, in 

 conjunction with the fibula, a large fossa for the 

 tibialis anticus and other muscles; and the 

 inner, facing also anteriorly, being a portion of 

 that surface of bone which is covered only by 

 skin and periosteum ; except at its upper part, 

 where three flat tendons pass upon it to be 

 inserted by the side of the tubercle in the follow- 

 ing order; that of the semitendinosus lowest, 



the gracilis next above, and the sartorius the 

 highest up and most anteriorly. The posterior 

 surface of the tibia at the supposed place of 

 section has advanced considerably forwards, so 

 as to leave a hollow for the popliteus muscle 

 which lies obliquely on this part of the bone. 

 A few lines below the great articulating surface 

 on the head of the tibia there are two things to 

 be noticed on its posterior aspect; at the outer 

 side a small articular surface for the head of the 

 fibula, and at the inner side a shallow pit 

 where the tendon of the semimembranosus is 

 inserted. 



The patella is a flat disk of bone placed in 

 front of the knee-joint; it equals in width the" 

 trochlea of the os femoris to which it is applied, 

 the posterior surface being for that purpose 

 covered with cartilage and divided into two 

 slight cavities by a prominent vertical line ; the 

 articular surface is oval from side to side and 

 does not reach to the lower edge of the bone. 

 Anteriorly, the patella is convex, and its hori- 

 zontal slightly exceeds its vertical measure- 

 ment, particularly in the female ; into its upper 

 edge are inserted the united tendons of the 

 rectus, cruralis, and vasti muscles ; into its 

 lower edge the strong ligamentum patellae 

 which joins it to the tubercle of the tibia ; it is 

 covered only by skin, fascia, and some ten- 

 dinous fibres, to which latter maybe attributed 

 the appearance of vertical striae observable on 

 the bone. 



( b.) Cartilages, ligaments, fyc. The whole 

 of the bony surfaces which come into contact 

 with each other or with the interarticular carti- 

 lages during the movements of the knee-joint 

 are covered with " cartilages of incrustation " 

 (see ARTICULATION); and the extent of these 

 on the condyles and trochlea of the os femoris, 

 on the head of the tibia and the posterior sur- 

 face of the patella, is well marked even in the 

 dry bones by their smooth and compact ap- 

 pearance and the total absence of foramina on 

 the parts so covered. Besides these pure car- 

 tilages there are two nbro-cartilages of a semi- 

 lunar form lying upon the head of the tibia, 

 which serve to deepen the articulating surfaces 

 for the reception of the condyles. These semi- 

 Innar cartilages, (cartilagines folcatd, s. lu- 

 nuta) as they are named, are thickest at their 

 convex edges which are attached rather loosely 

 to the circumference of the head of the tibia; 

 the concave edges are thin and sharp, and lie 

 unattached between the condyles and the tibia. 

 The two semilunar cartilages differ slightly 

 from each other in the two following points ; 

 the inner one is falciform, decreasing in breadth 

 from behind forwards ; the greatest width being 

 at the inner and back part, five-eighths of an 

 inch, whilst in front it is hardly more than one 

 quarter of an inch ; the anterior and posterior 

 cornua are separated to the distance of an inch, 

 whilst those of the outer semilunar cartilage 

 approach to within three-eighths of an inch of 

 each other; and, besides that the ring is thus 

 more nearly completed, the breadth of the outer 

 one is more uniform, being about three-eighths 

 of an inch throughout the greater part. The 

 thickness of either of them barely exceeds one- 



