DEVELOPMENT OP THE SKULL IN THE LACERTILIA. 
635 
I have felt this strongly in my own restricted held of work ; but, as much as in me 
lies, I have endeavoured that all my new terms should bear a filial relationship to the 
old familiar terms of human anatomy. 
In watching the metamorphosis of the skull, not forgetting the rest of the organs, 
in type after type of the Vertebrata, I am sustained and cheered by the hope, and 
even the prospect, of discoveries in this field, such as shall “make all things new” in 
the science. 
My fellow-workers, the Embryologists, both those who work at'the Vertebrata and 
those who choose the In vertebrata, are continually shedding the most welcome light upon 
my task: the present paper will show how much I value their work, and whether or 
no I have profited by it. 
It requires no little self-restraint to keep on digging about these special roots of 
one’s own selection, and not to go abroad over the whole field of Embryology. I trust, 
however, that this has been done in this and other papers of mine. 
About half the work of a Lizard’s growth has been done when we come to the 
first stage ; and yet these embryos were only the fifth of an inch long, measured along 
then greatest curve. 
And yet, here, at once, we are confronted with all that is distinctively Vertebrate ; 
all the knot and difficulty of harmonising these segmented forms with the segmented 
forms of the “Arthropods” is presented to us at once in the mere outline of a 
Vertebrate. 
Thus a large chapter in Embryology, proper, has to be read off before my work is 
be gim; I merely run along one of the lines marked out by my valued co-workers. 
But in starting from this point I am supposed to know what has been done up to 
that time, and in ascending the scale of stages in the growth of this selected region 
the metamorphosis of the whole organism has to be kept in mind, for nothing stands 
by itself, or is unrelated. 
This is true of this special type; but it is also to be considered that anything in the 
skeleton itself, as it develops and becomes metamorphosed, has to be thought of in 
comparison with its own proper “homologue” in all the Vertebrates below, as well as 
in all those above it. Thus, a single “ exoskeletal ” bony plate, such as the frontal bone, 
has to be considered in its uprise among the old Ganoid Fishes, and traced up to far 
beyond the Lizard, until its last and most perfect development is seen in our own 
species; this, assuredly, is the easiest thing in the whole business, and yet it involves 
no little labour and patience. 
I must remind the reader of the new light we are now getting upon the formation of 
the visceral arches, and their relation to the muscular segments and to the segmental 
nerves. The extension of the “ pleuro-peritoneal cavity ” into the head, and its 
subdivision and subsequent extinction there, and the formation of the pituitary body :— 
for all these matters I may refer to the descriptions here given, but still more to 
Mr. Balfour’s works. 
