CHAP. XVIII.] 



MEDIAN UNION : KIDNEYS. 



459 



before this part of the brain has widened out. In this way the auditory 

 involutions are approximated. This account however cannot apply to 

 all cases of union of ears; for the compounded ears are sometimes on 

 the ventral side of the neck, as in Guerdan's case 1 . 



The body of the symmelian ends posteriorly in an elongated lobe 

 made up of parts of the posterior limbs compounded together by homo- 

 logous parts. The two femora are usually united to form a single bone, 

 the tibise are separate and the two limbs are again compounded in the 

 tarsal region. The axial parts posterior to the hind limbs are always 

 greatly aborted 2 . 



Union of the kidneys in the middle line (Fig. 146), forming the 

 " horse-shoe kidney " of human anatomists, is a similar phenome- 

 non. As to the mode of development of this variation I know no 

 evidence. Usually the kidneys together form a single horse-shoe 

 shaped mass of glandular tissue, the union being posterior 3 ; very 



FIG. 146. Kidneys united in the condition known as "horse-shoe" kidney 

 (Man). In this specimen there were three renal arteries on each side. 



(From Guy's Ho*p. Rep., 1883.) 



1 See note 2, p. 458. 



2 See especially, MECKEL. Arch. Anat. Phys., 1826, p. 273 ; GEOFFROY ST 

 HILAIRE, Hist, des Anom., ed. 1837, n. p. 23; GEBHARD, Arch. Anat. Phys., 1888, 

 Anat. Abth., p. 164 (good fig.). To the determination of the morphology of the 

 hind limb the structure of the symmelian monster is of unique importance, but I do 

 not know that it has had the notice it deserves from comparative zoologists. 

 From the manner of union of the parts of the two limbs may be obtained a positive 

 proof of the morphological relations of the surfaces of the two limbs to each other. 

 In a symmelian the feet are united by their fibular borders, the minimi being 

 adjacent, the halluces exterior, and the combined plantar surfaces ventral. The 

 great trochanters are dorsal, being often united into one in the dorsal middle line, 

 and the patella are also dorsal, being also not rarely partly compounded. From 

 these facts, even were other indications wanting, we have a proof that if the hind 

 limbs were laid out in their original morphological relations to each other (as the 

 tail-fins of a Crayfish may be supposed to be) the halluces would be external and 

 anterior, the minimi internal and posterior, the flexor surfaces of the thigh and 

 crus and the plantar surface of the (human) foot would be I'entral and the extensor 

 surfaces of the thigh and crus and the dorsum of the (human) foot would be dorsal. 

 This is of course affirmed without prejudice to any question of phylogeny ; but that 

 these must be the ontogenetic relations of the parts is clearly proved by the symmelian. 



3 Sometimes anterior, e.p. ODIN, Lyon med., 1874, No. 12 [from Canstatt's 

 Jahresb., 1874, i. p. 19] ; and FREUND, Beitr. z. Geburtsh. u. Gyn., iv. 1875 [from 

 Canstatt's Jahresb., 1875, p. 340]. 



