EYE. 



171 



passage of the tendons of the peronaei muscles. 

 The apex of the malleolus is directed down- 

 wards, and is the point of attachment of the 

 middle external lateral ligament. 



Structure. This bone is very light and 

 elastic, a property rendered necessary by the 

 antagonist muscles which are inserted into its 

 opposite surfaces. Its extremities are composed 

 of cancellated structure, which extends some 

 way to the shaft of the bone. The medullary 

 canal, very narrow and irregular, is found only 

 in its middle third. 



Developement of the bones of the leg. The 

 tibia begins to ossify somewhat earlier than the 

 fibula. Both bones begin to ossify in their 

 shafts ; the ossific point of the shaft of the tibia 

 appeal's about the middle of the second month. 

 According to Meckel, in the embryo of ten 

 weeks, the fibula is not above half the length of 

 the tibia; after the third month the two bones are 

 nearly equal. Both bones have an ossific point 

 for each extremity. The superior extremity of 

 the tibia begins to ossify towards the termination 

 of the first year after birth. The inferior extre- 

 mity is ossified in the course of the second 

 year : the external malleolus is a prolongation 

 of the inferior extremity. The union of the 

 extremities with the shaft commences by the 

 inferior, and is completed from the eighteenth 

 to the twenty-fifth year. The ossification of 

 the fibula follows nearly the same course, 

 excepting that the superior extremity does not 

 begin to ossify till the fifth year. 



The tibia constitutes the principal pillar of 

 support to the leg. It is placed perpendicu- 

 larly under the femur, and as the latter bone 

 is inclined inwards, it follows that there must 

 be an angle formed between these two bones 

 at the knee-joint, a very obtuse one, with its 

 apex inwards.* It is then by the strength and 

 direction of the tibia that the leg firmly sup- 

 ports the body in the erect attitude ; the fibula 

 seems not to contribute at all to the solidity of 

 the limb, but is chiefly employed to increase the 

 surface of attachment for the muscles of the leg. 



The developement of the tibia and fibula in 

 the inferior mammalia is pretty similar to that 

 of the radius and ulna. The tibia is always 

 fully developed, and, as in man, is the prin- 

 cipal bone of the leg, its size being pro- 

 portionate to the weight and strength of the 

 animal. Admitting the fibula to be the ana- 

 logue of the latter bone, we find that, as it 

 is rudimentary in the Solipeds and Ruminants, 

 so the fibula is in a similar condition in these 

 animals. In the former animals this bone is 

 applied to the external side of the head of the 

 tibia in the form of an elongated stilet, termi- 

 nating less than half way down in a fine point. 

 On the other hand, in Ruminants it is only the 

 inferior part of the fibula that is developed ; it 

 appears under the form of a small narrow bone, 

 extending a very little way upwards, and form- 

 ing the external malleolus. 



* A preternatural obliquity of the femur causes 

 a corresponding divergence of the tibia from the 

 perpendicular. When the femur is directed un- 

 usually inwards, the tibia is directed downwards 

 and outwards. 



In Pachydermata the fibula is fully deve- 

 loped and quite distinct from the tibia, and 

 very small in proportion. In Edentata the 

 two bones are fully developed, and in the 

 Sloths the inferior extremity of the fibula con- 

 tributes to form the articular surface for the 

 astragalus. In Rodentia the two bones are 

 united together in the inferior half, as also with 

 the Insectivora, particularly in the Mole. In 

 many Carnivora these bones are fully developed 

 and detached : this is particularly manifest in 

 the Phocidae and the Felidae. In the Dogs r 

 however, the fibula is attached to the posterior 

 part of the tibia. 



For the description of the bones composing 

 the foot, we refer to the article under that 

 head; and for further details on the osseous 

 system of the extremities, we refer to the 

 articles OSSEOUS SYSTEM (Corap. Anat.) and 

 SKELETON. 



Abnormal condition of the bones of the extre- 

 mities. A congenital malformation of one or 

 more of the extremities is classed by Isidore 

 Geoffrey St. Hilaire among what he denomi- 

 nates " Monstres Ectromeliens," of which he 

 has three subdivisions: 1st, where the hands 

 or feet appear to exist alone, and seem to be 

 connected with the trunk without the inter- 

 vention of all or some of the intermediate 

 segments; these he denominates Phvcomeles, 

 (<puxv), Phoca, and /AE?U>?, membrum,} from their 

 resemblance to the permanent condition of the 

 aquatic mammalia : 2d, cases in which there 

 are one or more incomplete limbs terminating 

 in the form of stumps: to these he gives 

 the name Hemimeles: and, lastly, where the 

 limb or limbs are wholly absent or scarcely at 

 all developed. An interesting case of Phoco- 

 melia is recorded by Dumeril ; all the limbs- 

 were in this condition, owing to the absence 

 of the humerus, and forearm bones in the upper 

 extremity, and the presence of a very imperfect 

 femur, developed only as to the head and tro- 

 chanters, and a very imperfect tibia in the lower 

 extremity. The clavicle and scapula were pre- 

 sent, but presented some irregularities of form.* 

 The congenital absence of these last bones is- 

 rare excepting where the other bones of the 

 limb are also absent. 



It would be inconsistent with the objects of 

 this article to prosecute this subject further ; we 

 therefore refer for further details to the article 

 MONSTROSITY. 



For BIBLIOGRAPHY, see that of ANATOMY 

 (Introduction). 



(R. B. Todd.) 



EYE, (in human anatomy), opOaA/xo?, orga- 

 non vims ; oculus. Fr. (Eil ; Germ, das Auge ; 

 Ital.Orr hio. The human eye is a hollow sphere, 

 about one inch in diameter, with a circular 

 aperture in the anterior part about one-fifth of 

 this sphere in breadth, filled by a transparent 

 convex portion called the cornea, through which 

 the light is transmitted. Within this hollow 



* Bull, de la Soc. Philomath, t. iii., quoted in 

 Geoff. St. Hilaire 's Anom, de TOrganization, t. ii. 

 p. 211. 



