b. A less degree of malformation is when the superior part of the body is formed without the interior limbs. Fig.597. gives a represen tation of this monstrosity, of which a succinct account is to be found in my Handbook, D. ii. Bl. 100, and Tab. lxiii.
c. In a more perfect developement of the trunk one of the extremities may be wanting.
We call this malformation n2onopodia ; in it one of the inferior half-parts of the body has not been formed. It makes a transition to those monsters, in which the inferior ex tremity of the body tapers gradually into a tail-like form, which has given to them the name of monatra Sireniformia.
d. Sympodia or Siren-like form is the fourth species of defective formation of the trunk. The single inferior extremity is cony posed of the elements of two, and arti culates with a pelvis, which is not formed, as in rnonopodia, by one bone, but by a coalescence of two. In most of them the partially double, partially single inferior ex tremity terminates in a caudal point ; on account of which the name of Sirens has been adopted. To this imperfection are added closed anus, defect of external genital parts, and the existence of but one artery in the umbilical cord. The malformed inferior ex tremity has not always the same form. There fore we admit three varieties :— 1. Without a foot, Sirenomelia of J. G. St. Hilaire ; 2. With a single foot, more or less complete, Uronielia of J. G. St. Hilaire; 3. With a double foot. Fig. 622. represents the second, and fig. 623 the third variety.
By this survey of the four types of de fective formation of the trunk is proved that they form a very natural series, in which we are gradually inducted, from the total want of a trunk to monsters in which inversion of the inferior extremities is the only deviation from the natural form. The same regularity is here to be observed as in every other class of monstrosities. It is therefore impos sible to ascribe their origin to accidental ex ternal causes. Merkel has opposed his own peculiar and sarcastic wit to this absurd :etiology, and gives the very ludicrous ac count of a surgeon who supposed that the Sireniform monster had been formed during a very difficult delivery. If it is, on the
contrary, an original malformation, it may be asked, what can be its remote cause? Is it the original want of one of the umbilical ar teries? I should not think so; for one of these arteries is also wanting in the variety in which all the parts of the two, extremities are present, and we know that one of them may be wanting in a completely well-formed child. • (See p. 948.) Another question is, whether sympodia can be attributed to the coalescence of the inferior extremities (Meckel, Kamm, Boerhave, and Cruveilhier). Neither am I in clined to adopt this cause.
1. I cannot imagine a coalesence of bones so complete, that through these could be formed one single extremity.
2. It is impossible to explain by it the im perfect condition of the leg and of the foot in the majority of cases.
3. From such a fusion or coalescence can not be derived the imperfect state of the rectum, and of the sexual and uropoietic or gans.
It seems to me more probable that sym podia is due to some original malformation of the pelvis and its viscera, of which the cause remains unknown. The formation of a head solely, of an incomplete trunk without the lower limbs, or of a single inferior ex tremity, is certainly to be attributed to nothing else but impeded developement. It shows, moreover, that the different parts of the body are quite independent of each other in their original formation.
e. Original defective formation of the pelvis.
In a well constituted body the pelvis may be originally malformed, as is proved by the ob liquely narrow pelvis of Nazele, and by the transversely narrow pelvis of Robert ; of which malformation the cause is to be found in the imperfect formation of the sacrum.
f. Defective development of the spinal column. This has been principally observed in calves. It is too short, defective, more or less incurvated, and some of the vertebrm fused together. The head is situated at a short distance from the thorax ; the tail and the anus are reflected to the dorsal surface; the pelvis is too narrow, and turned upwards at its posterior part.