DEVELOPMENT OE THE SKULL OE THE COMMON FOWL. 
801 
the latter processes lie near the rostrum, and are enveloped in the same stroma ; this 
projecting part forms an imperfect septum between the middle nasal passages ( m.n .), 
which open into each other below (compare this figure with Plate LXXXII1. fig. 10, jp.e., 
g>.a., r.st.). 
The whole nasal labyrinth is continuous ; the prefrontal wall, the outer wall, the tur- 
binals, and the alee nasi are all developed from that tract of the primordial skull which 
curls downwards, in front of the pituitary space, into the frontal wall of the embryonic 
skull (Plate LXXXI. figs. 1 & 2). 
This free growth of cartilage into so many morphological territories is correlative to 
the simplicity of the tissue, which rises but a step or two beyond protoplasm, is ready 
to be metamorphosed into any other skeletal tissue, and yet serves as a persistent ske- 
leton to many parts, especially those of the nasal labyrinth. 
The quadrate end of the pterygoid is lined with flat-celled hyaline cartilage (Plate 
LXXXYI. fig. 12, c.), and the contiguous osseous tissue (o.) is formd by endosteal meta- 
morphosis of more swollen cells. 
When the cartilage-cells of the articular facet are viewed endwise (fig. 13, c.), they are 
seen to have an oval outline. The meniscoid facet has not changed, except in size, since 
the time of hatching. 
Tenth Stage. — Fowls several years old. 
By the time the young Fowl is a year old most of the cranial sutures are completely 
closed; and then, year by year, the skull becomes more and more dense, the periosteal 
layers filling-in every vacant space not needed for the transmission of vessels and 
nerves. 
Thus in the skull of an aged bird (Plate LXXXVII. figs. 4-10) the occipital, otic, pos- 
terior and anterior sphenoidal, and the ethmoidal regions have become one continuous 
bone, with the old landmarks all removed, and scarcely a sign left of its once highly 
complex condition. 
This state of things, for a bird, is quite normal ; and although carried to a very high 
degree in the Fowl, yet in some more typical birds the obliteration of all signs of the 
once composite condition of the skull is still more perfect. 
The present paper is linked on to the first by the description of the skull in the 
aberrant Struthionidse (Tinaminae, or Dromseognathse) ; in those birds there is some falling 
away from what is typically struthious, and some approach to what we have here in the 
higher Gallinse. In the skull, however, the Tinamous, wherein they diverge from the 
Ostrich-tribe, do not equally approach the Gallinse, but rather show affinity to the 
Charadriomorphous types. 
This, however, is not all ; for the Tinamous have a tincture of the Reptilian nature 
in them ; and whilst the sutures close very perfectly in the Ostrich, as in the Fowl and 
other typical birds, in them several of the most important of those landmarks remain 
throughout life (see First Paper, pp. 174-178, Plate xv.). 
mdccclxix. 5 o 
