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The anatomy of a double pig (syncephalus thoracopagus).

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AUTHORS' ABSTRACT OF THIS PAPER ISSUED
BY T H E BIBLIOQRAPHIC SERVICE OCTOBER
6.
THE ANATOMY OF A DOUBLE PIG (SYNCEPHALUS
THORACOPAGUS)
8. R. WILLIAMS -4ND R. W. RAUCH
Miami University, Oxjord, Ohio
SEVEN FIGURES
In 1895, a double pig was born dead on the farm of Craig
Brothers, Oxford, Ohio, breeders of Poland China stock. The
specimen was collected by Prof. A. L. Treadwell and left in
the laboratory of Miami University. Except for opening the
body cavities no work was done on the pig until in the fall
of 1916. The appearance of the article on a monster pig by
Carey in The Anatomical Record on February, 1917, renders a
detailed description of our specimen unnecessary. We present,
therefore, a brief outline only, describing the peculiarities of
this double monster.
Figures 1 and 2 are photographs of the animal from the dorsal and the ventral sides. As in Carey's specimen there has
been a separation of the growing points of the embryo into two
parts, probably two primitive streaks formed side by side, and
then a fusion of the adjacent parts of these two growing points
to form the monstrosity.
According t o Adami and McCrae, p. 68, in double monsters
there is first of all a complete cleavage and then a secondary
fusion of contiguous parts. This results in this case in the
production of a mono-symmetrical janiceps with a perfect
ventral face and a rudimentary dorsal face not recognizable as
such. The fusion continues through the thoracic region but
the bodies are separate above the abdomen and as nearly as
we can tell from the specimen (which was opened in 1895) there
are two umbilical cords. This, however, is not certain. The
reception of two blood supplies from the mother is exceptional.
273
274
S , R. WILLIAMS AND R. W. RAUCH
The urinogenital organs are paired and normal in each body.
The specimen is of the male sex. In the pig described by Carey,
the heads are fused side by side with one head turned to the
left and one to the right. If the head of our specimen has been
formed in the same way, there has been a much greater degree
of regulation, the essential suppression of the face turned to the
ABBREVZATIONS
Ao.R., right aorta
Ao.L., left aorta
A . V . C . , anterior vena cava
Card., cardiac end of stomach
Cart., cartilaginous bond betwccn the
two bodies i n the region of thc anterior end of thorax (so called dorsal
side)
Ce., cecum
Cleft., division of anterior end of
tongue
L., left body
Par., partition in
roof of mouth
from ‘dorsal’ t o ‘ventral’
Pul.L., lcft pulmonary artery from
left aorta
PuZ.R., right pulmonary artery from
right aorta
P.V.C., posterior vena cava
Pgl., pyloric end of stomach
R., right body
Rud.F., rudimentary face
Sp.C., spinal cord, left
Vert., atlas and axis of right vertebral
column
ANATOMY OF A DOUBLE PIG
275
right (dorsal) and the development of the external form of the
head with reference to the face turned toward the left (ventral).
AI,IR/LENTARY SYSTEM
Figure 3 is a diagram of the structures of the alimentary
system. At the tip, the tongue is double, a cleft extending for R
short distance back in the mid line. Further back behind the
tongue, there is a connective tissue partition which extends
from the roof to the floor of the pharynx. The two spaces
formed by this partition unite again, when the latter stops,
into a small cavity which is continued back as the single esophageal lumen.
The slender tube of the esophagus extends back to an opening on the posterior and dorsal side of the large stomach. This
organ has a longitudinal constriction in its middle indicating its
double origin. The intestine leaves the anterior ventral side
of the stomach and turns posteriorly as a single slender coiled
tube 42 inches in length. This connects with a transverse tube,
276
S. R . WILLIAMS AND R. W. RAUCH
3
/.
\\
'P.V.C.
4
'
ANATOMY OF A DOUBLE P I G
277
at each end of which is a cecum, the beginning of the two large
intestines. The large intestine for the left body is 103 inches
long and the one for the right smaller body is 9 inches in length.
There is one spleen found in the body of the left pig. Possibly
the fact that the liver mass in the right body is two to three
times the volume of that in the left may have to do with the
absence of symmetry in the spleen. This explanation will not
hold, however, for the pancreas, which, though poorly preserved is single. It lies by the duodenum and in the right body
cavity. The liver is all connected dorsally but free ventrally
and, as stated above, most of it is on the right side.
BLOOD SYSTEM (FIG. 4)
The heart is a fused structure with two large thin walled auricles
and two large ventricles with equally thick walls. The auricle
of the right side receives directly the single anterior vena cava
from the head and anterior extremities. The auricle on the
left side is connected with a dorsal sac, possibly a sinus venosus,
which also has a passageway into the right auricle. All the
blood from the posterior part of both bodies comes into this
sinus through a vessel we have called the posterior vena cava.
There is a passage way from each of the auricles into the ventricle of its own side. The ventricles are distinct with a thick
partition between and each ventricle sends a large aorta to the
body on the opposite side, these aortas crossing just anterior to
the heart. The aorta from the left side supplies blood to the
head while that from the right side sends no branches farther
forward than the fore legs. Possibly this may explain the
difference in the siae of the two bodies. If approximately half
the blood was pumped by each ventricle, the left body would
have been better fed since none of its blood is sent to the head.
The aorta to either side sends a branch artery to each fore
leg of the body it supplies. These legs are at different levels
(figs. 1, 2) and between the two branches of each aorta there is
given off a small branch to the lung, a pulmonary artery (fig. 4,
PuLR, PULL). These pulmonary arteries pass to the lung
complex which is fused dorsally and free ventrally. On the right
side there are three lobes and on the left four lobes of the lung.
278
S.
R. WILLIAMS AND R. W. RAUCH
There is but one trachea not two as in the specimen described
by Carey.
SKELETOX (FIG. 5 )
The skull is shaped much like that of a normal pig. On the
dorsal side is a fontanelle covered with a mass of wrinkled skin
representing the rudiment of a face and bound t o the brain by
connective tissue strands which are part of the dura mater
(Rud F. Figs. 1, 2, 6, 7). There are two separate vertebral
columns with three points of attachment to the skull, the central one being common t o each column (fig. 6). There is a
central bony niass between the two atlases and probably derived from them, which makes part of the middle articulation to
the skull. The second and following vertebrae in each body
axe nearly like those in normal pigs.
ANATOMY OF A DOUBLE PIG
6
7
279
280
S. R. WILLIAMS AND
R. W. RAUCH
There are thoracic ribs on the dorsal side some of which may
connect to the cartilaginous mass (Cart, fig. 6) which connects
the two bodies dorsally. It is possible that this is part of a
sternum. At any rate, the ventral ribs and sternum are more
nearly normal.
KERVOUS SYSTEM (FIGS. 6, 7)
The single cerebrum is slightly larger than that of a pig of the
same size, having a ‘disturbed’ area in the region just below the
dorsal rudimentary face. In dissecting off the skull cap shown
in figure 7 no identifiable brain tissue was cut, simply connective
tissue such as composes the dura.
The cerebellum is normally placed and presents three lobes,
one median and two lateral. The medullas are fused to each
other and from each a normal spinal cord extends posteriorly.
SL7MRlARY
The dissection of this monster pig is presented because it
differs in many respects from that described by Carey, in some
points being more fused, in others being more distinct.
1. The head is more nearly normal with but two ears, two eyes
and two nostrils.
2. The alimentary canal has a divided pharynx, a grooved
stomach, a single pancreas and a single spleen.
3. The trachea is single, connecting to a ventrally lobed lung
mass.
4. The heart is fused, with a single venous system. The
arterial supply of the head is from one side of the heart only.
5. The nervous system is fused to a much greater degree,
there being complete separation in the spinal cords and fusion
from the medullas anteriorly.
We wish to thank Dr. A. L. Treadwell for the privilege of
dissecting the pig, and Dr. J. A. Culler for making the skiagraph.
LITERATURE CITED
ADAMI,J. G. AND MCCRAE,J. 1912 A text book of pathology, pp, 759.
C ~ R E YE., 1917 The anatomy of a double pig, Syncephalus thoracopagus with
especial consideration of t h e genetic significance of t h e circiilatory
apparatus. Anat. Rec., vol. 12, pp. 177-191
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