Yay! Another series, and more of a break. This time, it’s about terminology, one of my more favorite aspects of methodological science. Without knowing what to name stuff, we lapse into grunting and rude gestures, and nobody likes that. Well, I mean, I guess some of you do — perverts.
But terminology has two broad aspects, and in most cases, they are both highly useful, but you need to keep an eye on them.
1. Terminology must be concise (structure): You have to know that a term will often affect a broad range of things, while at the same time you want to keep an original concept original.
2. Terminology must be intuitive (form): You have to get nomenclature to use it, and a person who cannot grok that term will not understand it, regardless of how precisely you’ve used it. (You see what I did thar?)
This prefaces our introduction to terminology.
Phalanges are those bones or bits in your fingers and toes, and they often move around; they let you grip, maintain balance while standing, provide leverage while walking, and can be used as singalling devices. Different groups call different digits different things (like fingers, digits, or polleces). Sometimes, a system will use the same terminology, but connect the terms to different types of digits under different schemes. While this is not always a problem, it runs us afoul of point 1, and this is especially true of avian digit homology of the wing (also called “arm” or “forelimb”). There are even problems when, dealing in homology, sometimes what is originally one type of digit becomes another, and the terminology shifts (or doesn’t) when it should do the other under the argument being used (also apparent in avian digit numbering, but then this system becomes problematic when dealing with things like vertebral identity in vertebrates from fish to amphibians to reptiles to mammals).
Here I will present a scheme:
(a) The anterior and posterior limbs in tetrapods are the only motile limbs in any vertebrate that bear digits (mutants don’t count, and those are generally duplicates of standard limbs anyway and will follow the scheme for that limb);
(b) The anterior limb will be called just that (but it is also the forelimb or arm, depending on your group) and will be abbreviated AL, while the posterior limb will be called that as well (but is also a hindlimb and leg), regardless of whether you’re human, and is abbreviated PL;
(c) The manus is the digit-bearing extremity of the forelimb, and is the anterior autopodium, but when talking about the classic manus in isolation of the carpal system or limb we can also use just manus (m), and consequently the posterior autopodium is the pes (p);
(d) Bone sets between the limbs are simplistic: Carpals (C) and tarsals (T) are coordinated in some groups with metacarpals (MC) and metatarsals (MT, and are numbered using the Roman numeral system (I, II, III, etc.) with the exception of elements that do not follow a regular serial system (e.g., mammals); abbreviations labelling names of bones are capitalized, while element segments of the autopodium are not (e.g., MTII);
These terms are essential for prefacing the basic layout for phalangeal terminology, which is slightly more complex:
(e) All digits are numbered serially from the first to the last following the Roman numerals and are listed after the label “d” (e.g., dI, dII); further, all digits are listed under their autopodial designation (mdI, pdII, etc.) where “m” means manus and “p” means pes;
(f) All phalanges are numbered serially from the base to the last element of the digit, regardless of whether it ends in an ungual (“claw”) and follow the Arabic numeral system (1, 2, 3, etc.) following a dash (to separate the two numbers clearly), such that the first phalanx of the first digit is dI-1;
(g) Where left and right material is distinguished, the preface “r” and “l” followed by a dash and then by the designation is used (e.g., r-mdII-3).
Finally, a graphical representation of this idea. An additional notation is used, which may or may not be useful: I apply the label “u” after the phalanx number to indicate it is an ungual, i.e., a terminal phalanx modified to bear a nail or claw. Such a phalanx is generally modified from another phalanx, termed intermediate, by the absence of a distal articulation and is usually expanded or otherwise differentially shaped.
I should also like to draw attention to the debate on the digital homology of birds, which has been shown to correspond to diapsid digital condensations in crocodilians and mammals as digits dII-III-IV, while the digits are modified as to correspond morphologically to dI-II-III. Under this scheme, regardless of the homology issue, the phalanges have the morphology and identity of dI-II-III, and that is suggested here for workers who find this post of any importance. The reason for this is that it is not actually certain where, in the development of Theropoda, the identity shift from I-II-III to II-III-IV occurs, despite recent work  indicating an apparent fossilized portion of the shift, which has been rebutted  on the basis of other homological data. I have little to say on this matter.
Note: Notation aside, terminology for phalanges is pretty cut and dry, although there are interesting corrolaries; in birds, there is a system of terms for the position and relation of the phalanges to one another, and some of these terms (such as syndactly) have been used for mammals as well. Other terms, though, are generally universal.
Pollex – This is generally used for the first manual digit, mdI, also called the “thumb” in humans. It is not generally regarded as a finger in humans (e.g., the phrase “finger and thumbs”), and is called the alular digit in birds.
Hallux – This is generally used for the first pedal digit, pdI, and also called the “big toe” in humans.
Intermediate phalanx — Any phalanx that is not terminal or an ungual, or is the first phalanx in a digit’s series.
Proximal phalanx — This first phalanx in a series of at least two; if the phalanx is by itself, it’s generally terminal.
Terminal phalanx — The last phalanx in a digital series, often modified into an ungual; in some cases, this phalanx is unremarkable, and is not ungulate in form, but just a nubbin.
 Xu X., Clark, J. M., Mo J., Choiniere, J., Forster, C. A., Erickson, G. M., Hone, D. W. E., Sullivan, C., Eberth, D. A., Nesbitt, S., Zhao Q.-l., Hernandez, R., Jia C.-k., Han F.-l., and Guo Y. 2009. A Jurassic ceratosaur from China helps clarify avian digital homologies. Nature 459:940–944.
 Vargas, A. O., Wagner, G. P. & Gauthier, J. A. 2010. Limusaurus and bird digit identity. Nature Precedings