TERATOLOGY. 



971 



the left of the other, proceed towards the an- 

 terior and posterior aspects, and are there 

 connected with an anterior and posterior 

 sternum. The best idea of the construction 

 of this osseous fabric may be formed by sup- 

 posing the two complete chests of two bodies 

 to be set one against the other, and that then 

 the anterior extremities of the right ribs of 

 the right body, and those of the left ribs of 

 the left body, unite with one sternum arid 

 pull it forwards, while, in the same manner, 

 the left ribs of the right body, and the right 

 of the left, unite on the posterior aspect 

 with the other sternum, and carry it back- 

 wards. The consequence is, that the two 

 vertebral columns are turned away from one 

 another, and that the parts above and below 

 the thorax are double. By the formation of 

 this common thorax, the lateral is distin- 

 guished from the anterior duplicity, in which 

 the thoraces are commonly connected only 

 by the points of the sterna, and, as to their 

 cavities, are separate. And with these diffe- 

 rences of external construction, others not 

 less important, of internal arrangement, coin- 

 cide, which fully justify the separation of the 

 two forms, however similar the external ap- 

 pearances of many of the examples of either 

 may be. 



The numerous varieties of lateral duplicity 

 may be divided into two principal sets. The 

 first begins with the complete duplicity of the 

 whole body, and ends with its perfect sin- 

 gleness; in the second, the duplicity of the 

 body remains, but the head gradually becomes 

 single. The forms included herein, of which 

 1 have given ample accounts elsewhere, may 

 be briefly summed up as follows. 



1. Complete duplicity: all the external 

 parts and sometimes the abdominal and pelvic 

 viscera double, one common double-sized 

 thoracic cavity, formed in the manner just 

 described, and containing four lungs, and (in 

 all cases with which I have been acquainted) 

 onl} r one heart. The examples of this form 

 are very numerous, and are to be met with in 

 all the large museums of Europe. 



2. In the examples of this second group, 

 which exhibits the first step towards single- 

 ness, one of the sterna may be traced in a 

 succession of specimens, becoming gradually 

 narrower, and permitting a closer approxima- 

 tion of the two corresponding upper extremi- 

 ties, till, in some examples, they are com- 

 pletely united, and there are found only three 

 limbs above, with three or four below. The 

 two juxtaposed scapulae, for example, are 

 merged into one, or they remain separate, 

 but have only one humerus between them, 

 and this splits below, to articulate with two 

 fore-arms ; or there is but one fore-arm, 

 and this bears supernumerary fingers. In 

 short by a great variety of modes there is a 

 general tendency towards union of two of the 

 upper extremities. 



3. In the third group we have a repetition 

 of the same series of changes in the lower 

 limbs, as in the second was traced in the 

 upper ; here, as there, presenting numerous 



varieties, in the last and lowest of which only 

 three lower limbs, and the third of these ill- 

 formed, are found. 



4. The third limb has now gradually disap- 

 peared, and, with a complete duplicity above 

 the pelvis, there are but two limbs below it, 

 and these well formed. In this class is placed, 

 with many others, the Ritta-C/iristina monster, 

 described by Serres, which lived to eight 

 months, and the still more remarkable ex- 

 ample mentioned by Buchanan, of a two- 

 headed man, 28 years old, who lived in the 

 reign of James III. of Scotland. 



5. The union proceeding, and this simpli- 

 city of the lower part of the body being re- 

 tained, examples come next in which the 

 upper parts also are united ; the two super- 

 fluous upper limbs being united into one, pre- 

 senting a single upper-arm, with a double 

 fore-arm and hand, or a single upper-arm, 

 fore-arm, and hand with ten fingers, or only a 

 mal-formed limb, or a mere projection, occu- 

 pying the place of the superfluous limbs. 



6. Even this last indication of duplicity of 

 the upper parts ceases, a scapula only remains, 

 or this also is absent ; and next, one of the 

 sterna having disappeared, and the vertebral 

 columns having been connected on the corre- 

 sponding side by their respective ribs united 

 into single arches, these now become gradually 

 shorter, and the columns approach each other 

 more and more nearly, till they are connected 

 by only a cartilaginous substance in the place 

 of ribs, or are at some part fused together. 



7. In this next group both the upper and 

 lower parts of the body are single ; the ver- 

 tebral column is single below the cervical 

 region, or exhibits only a trace of duplicity 

 (to which something similar is often presented 

 by the sternum), but at the cervical region 

 becomes double, and on each portion bears a 

 head. Of this also I have published many 

 examples. 



8. In the eighth group the extent of that 

 cervical part of the column which is double 

 becomes less and less. 



9. In the ninth group, the two heads are 

 seated on an apparently single neck, in which 

 all the cervical vertebrae are single, or only 

 bear traces of duplicity, except the first two, 

 or the first alone. 



10. Hitherto the duplicity of the head was 

 perfect ; in this group the two heads also 

 begin to coalesce, and, in a considerable num- 

 ber of cases, gradations are traced in which 

 the adjacent ears are very closely approxi- 

 mated, and the heads are united behind. 

 Then there are cases in which one ear only is 

 placed between the adjacent surfaces of the 

 two heads, and this disappears gradually, and 

 at last totally. Next in order are the cases in 

 which the adjacent ears being lost, the two 

 adjacent and middle eyes first become very 

 close, and then occupying one orbit finally 

 coalesce. Next come those case* in which 

 there is such a union of the heads, that the 

 two upper jaws are articulated with one lower 

 jaw ; and, lastly, those in which the head is 

 doubled only in individual parts or in which 



