Picture - Cosmic Polymath

326 DESIGN IN NATURE
PLATE LXXXV (continued)
Fig. Y.—Spiral shell with right-handed spiral whorl at the apex. The whorl consists of two parts which twist and plait into
each other. It resembles a right-handed spiral nebula (Plate viii., Pig. 4); spiral seeds (Fig. 11, D, B) ; spiral spermatozoa
(Plate xii., Fig. 1, E), &c. (the Author, 1859, and subsequently).
Fig. 8.—Photograph of a dissection by the Author of the left ventricle of a sheep's heart showing the posterior surface and
apex of the left ventricle. The left ventricle of the heart of the mammal is composed of two sets of spiral muscular fibres. /, h,
the two sets of superficial spiral muscular fibres form the first external layer. They are seen involuting or turning into
the left apex to make a most exquisite whorl. Compare with Fig. 7 of this Plate. It is these two sets of fibres which are chiefly
concerned in the production of the two musculi papillares. The whorl formed by the two sets of spiral muscular fibres of the left
ventricle of the heart of the sheep is quite as distinct in the left ventricle of the human heart.
« .^
I'iG. 67.
Fia. 67 (A, B, 0, D, E).— Represents a series of original dissections and drawings by the Author, showing the distribution of the
muscular fibres in the oesophagus, stomach, pyloric valve, and duodenum.
A. Minute dissection of the muscular fibres of the oesophagus of the horse. In this dissection no fewer than seven layers of
muscular fibres can be made out. The distribution is similar to that met with in the left ventricle of the mammalian heart The
fibres are spirally arranged, and consist of three external sets, three internal sets, and a central layer. Proceeding from without
inwards the following are encountered—an external longitudinal layer (a, n', a'), an internal ditto (e), a slightly oblique external and
a slightly oblique internal layer which cross each other (h, V), a very oblique external and a very oblique internal layer which also
cross (c, c'), and a transverse or central layer (d, d'). This muscular mechanism is endowed with centrifugal and centripetal powers
whereby it opens before and closes behind the bolus in swallowing, with the result that the food is enforced into the stomach. The
scheme of the mechanism is indicated at D, E, of Fig. .3, Plate Ixxxiv.
In vomiting, the swallowing process is reversed ; the arrangement working efi'ectively in both cases. One can eat ' swallow '
and drink with the body inverted.
The swallowing process is similar to that induced in the teat of the cow in milking. According to prevailing views the interior
of the oesophagus is irritable, and the bolus of food acts as a stimulus which causes the oesophagus to open and close rdternatelii and
so transmit it to the stomach. This cannot be the true explanation. The passage of the bolus into the stomach is a continuous
movement, and cannot possibly produce the alternating, interrupted movements which characterise the ojsophagus If moreover
the bolus acted as a stimulant it would cause contraction of the oesophagus in front instead of behind itself. The oesophagus would
B