216 NATURAL HISTORY SOCIETY OF DUBLIN. 
EXPLANATION OF PLATE Xf. 
Fig. 1. Mass of Tubipora musica, nat. size. 
Fig. 2. ‘The same to show the buds. 
Fig. 3. Polyps, seen from above, three expanded ; from the side of the retracted polyp, 
which is seen in the lower part of the figure, between the two expanded 
polyps, will be found the lateral fold-like prolongation of the tube referred to 
in the text. 
Fig. 4. Polyps in different stages of expansion and retraction; at ¢ the lateral fold-like 
prolongation is seen. 
Fig. 5. Mouth, with circular lip and four tentacles studded with spicules. 
Fig. 6. A section through tube and polyp, the latter fully retracted. 
Fig. 7. Lenticular spicules from the tentacles. 
Fig. 8. Fusiform spicules, plain and warty, from ectodermic layer between base of ten- 
tacles and edge of hard tube. 
Fig. 9. Warty fusiform spicules. 
Fig. 10. The same, gradually becoming coalesced, and forming a rough irregular net- 
work at one spot; in another becoming solidified. 
N. B.—All the figures on this Plate have been drawn by Mr. Ford, from specimens 
preserved in spirits. It need not be said that they are accurate representations of the 
structures thus preserved; yet they would undoubtedly have been much more life-like 
had they been drawn by Mr. Ford from living specimens. Figure 3, however, is not 
only an accurate, but also to my mind a life-like drawing. 
ALEXANDER Macalister, Demonstrator of Anatomy, Royal College 
of Surgeons, Ireland, read the following Paper :— 
On THE ARRANGEMENT OF THE PRoNATOR Muscles IN THE LiImpBs oF 
VERTEBRATE ANIMALS. 
In most vertebrate limbs a group of muscles exists, for the production 
of motion between the two parallel bones composing that limb segment 
which is the second from the shoulder girdle; and as the pectoral ex- 
tremities of animals are usually more perfect than the pelvic in point 
of development, being often more or less subordinated to the use of the 
head, this group of muscles consequently, as a rule, preserves a more 
perfect individuality in the fore limb than in the hinder. 
For obvious reasons, many animals are incapable of the actions of 
pronation and supination; but it does not necessarily follow that in 
such these muscles should become completely suppressed, for in many 
instances of the kind subordinate functions assume the preponderance, 
and action changes accordingly. 
The group of muscles under consideration consists of two series— 
pronators and supinators. To the former of these we will limit our 
attention at present. When fully developed, the pronators are two— 
first, a long pronator (epitrochlo-radial); and, secondly, a short trans- 
verse muscle (ulno-radial). 
ist. The long pronator, or pronator radii teres, is one of the most 
regular and invariable of limb muscles. In man its origin is from the 
inner condyle of the humerus, on a plane superficial to that of the other 
flexors (its second head is of a different nature, as shall be seen here- 
after). In all the Quadrumana its origin is similar, but its difference 
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